Mohs Surgery

Updated: Apr 29, 2022
Author: Shang I Brian Jiang, MD; Chief Editor: Arlen D Meyers, MD, MBA 


Practice Essentials

Mohs surgery is a surgical technique used to treat various skin cancers that allows precise microscopic control of the margins by utilizing tangentially cut frozen-section histology. Mohs surgery has become the treatment of choice for most skin cancers on the head and neck, as well as for recurrent or histologically aggressive lesions.

A retrospective study by Reeder et al of the use of Mohs surgery from 1995 to 2010 in the United States found an upward trend in the technique’s utilization but a low percentage of skin cancers (10% on average) being treated with this surgery. The study, which drew data from the National Ambulatory Medical Care Survey, also indicated that Mohs surgery most often involved the head and neck region.[1]


See the list below:

  • Fresh-tissue technique: Treatment of choice for most skin cancers on the head and neck as well as for recurrent or histologically aggressive lesions; cutaneous tumors are excised at a 45° angle with mapping and subsequent identification of residual cancer using light microscopy

  • Fixed-tissue technique (chemosurgery) (used infrequently): Similar to the fresh-tissue technique, but tissue fixation is achieved with a zinc chloride paste and takes place before excision; this process eliminates the need for anesthesia and creates a blood-free surgical field

Indications for Mohs surgery

All recurrent basal cell carcinomas (BCCs) or high-risk primary tumors with 1 or more of the following features are candidates for Mohs surgery:

  • Aggressive histologic growth pattern

  • Location in anatomic sites at which conventional treatment modalities have a higher potential risk of recurrence

  • Location at anatomic sites that require tissue conservation for optimal reconstruction

  • Other features

Squamous cell carcinomas (SCCs) at high risk for local recurrence or metastasis are best treated with Mohs surgery. High-risk criteria include the following:

  • Large size (>2 cm)

  • Depth of invasion (>4 mm)

  • Recurrent or incompletely excised tumors

  • Histologic subtype, including undifferentiated, poorly differentiated, acantholytic (pseudoglandular)

  • Perineural or perivascular invasion

  • Rapid growth

  • Long duration

  • Tumors in patients with immunosuppression

  • Radiation-induced lesions

  • Certain genodermatoses (inherited skin conditions)

  • Certain anatomic locations (eg, scalp, periorbital/canthal region, columella, lips, lower extremities, nail bed and matrix)

  • Other sites (eg, previously irradiated skin, thermal/radiation scars)

Other unusual cutaneous tumors with aggressive features or highly cosmetically sensitive locations are candidates for Mohs surgery, including, but not limited to, the following:

  • Verrucous carcinoma

  • Keratoacanthomas

  • Extramammary Paget disease

  • Microcystic adnexal carcinoma

  • Dermatofibrosarcoma protuberans

  • Sebaceous carcinoma

  • Atypical fibroxanthoma

  • Malignant melanoma

Disadvantages and limitations of Mohs surgery

Disadvantages of Mohs surgery include the following:

  • The procedure may become tedious and prolonged for the patient; especially if the case is difficult or complex.

  • An inability to remove a large or difficult tumor in one day may preclude immediate reconstruction after complete excision.

  • The procedure requires a specially trained dermatologist and ancillary personnel.

  • Multiple injections of local anesthetic can cause patient discomfort.

Limitations of Mohs surgery may include the following:

  • Noncontiguous tumors and/or disconnected foci in tumors may result in recurrence.

  • Adjunctive therapy may be necessary to ensure cure.

  • The extent of the tumor may be too great to be amenable to surgery.

Preoperative evaluation

Issues to consider and evaluate prior to Mohs surgery include the following:

  • Patient’s general health, history (including medications, allergies, previous surgeries/hospitalization, potential complicating conditions such as diabetes, cardiovascular/pulmonary compromise, history of prolonged bleeding, or tendency for keloid/scar formation)

  • Review of the skin tumor’s gross appearance and histologic features

  • Discussion with patient regarding Mohs surgery technique, alternative therapeutic options, potential complications from the procedure, and postprocedure wound care and reconstructive options

  • Discussion with patient about cessation of alcohol and/or tobacco use during the perioperative period

  • Discussion with patient about food, medications, and attire on the day of surgery, as well as postoperative issues

  • Interdisciplinary consultations (eg, dermatology, pathology, cutaneous/oncologic surgery, reconstructive surgery)

Mohs fresh-frozen technique: general, basic procedure

See the list below:

  1. Outline the tumor; then administer local anesthesia.

  2. Debulk the tumor with a curette to delineate the tumor extent (Note: This is less effective with morpheaform BCCs or other nonfriable tumors).

  3. Tattoo or mark the tumor for precise orientation of the tissue specimen.

  4. Excise the tissue (a) with the scalpel angled 45° to the skin (to bevel the edge to facilitate histologic processing); (b) circumferentially around the tumor at a 45° angle; and (c) under the skin, parallel to the surface, so that the deep margin is excised horizontally.

  5. Achieve hemostasis with spot electrodesiccation, suture ligatures, oxidized cellulose (eg, Surgicel, Oxycel), pressure, or other methods.

  6. Draw a 2-dimensional (2-D) map of the patient's skin defect; include the tattoos/marks that were used to orient the specimen.

  7. Divide the tissue along the tattooed or scored lines, and invert the tissue (dermis turned up); then, color code the edges of the specimen with tissue dyes.

  8. Mount the tissue, flattening the undersurface in an even horizontal plane; use a cryostat to cut 5- to 7-µm horizontal frozen sections of each tissue specimen; and place the specimens on slides.

  9. Stain the slides (usually with hematoxylin-eosin or toluidine blue), and interpret the results.

  10. Mark any residual neoplasm in red on the 2-D map of the patient’s skin defects; remove the additional tissue where residual tumor has been identified.

  11. Immediately reconstruct the resulting postprocedure defect.

Mohs fixed-tissue technique (infrequently used)

See the list below:

  1. Debulk the tumor with a curette, and apply dichloroacetic acid.

  2. Apply a layer of zinc chloride paste (fixative paste).

  3. Cover the fixative paste with an occlusive dressing for 6-24 hours.

  4. After tissue fixation, perform the fixed-tissue surgical technique similarly to the fresh-tissue technique (ie, with the scalpel angled 45° to the skin, make an incision in the fixed tissue near the border of the unfixed tissue, and continue in the fixed tissue parallel to the skin surface); then, examine the tissue sections under microscopy, and apply additional fixative paste to any remaining areas of tumor involvement for another 6-24 hours.

  5. Excise any residual tumor in the same manner as the fresh-tissue technique, generally at a rate of one stage of excision per day.

  6. After achieving a tumor-free defect, allow the remaining fixed tissue to slough (the process generally takes a few days).

  7. Repair the defect or allow it to heal by means of secondary intention.

Potential complications

See the list below:

  • Bleeding

  • Nerve damage

  • Infection

    Mohs surgery is generally indicated for the treatm Mohs surgery is generally indicated for the treatment of tumors in areas where a high risk of recurrence exists and cosmetic results are critical.


Introduction, history, and training

Mohs micrographic surgery (MMS), or Mohs surgery, is a surgical technique used to treat various skin cancers that allows precise microscopic control of the margins by utilizing tangentially cut frozen-section histology. In this procedure, cutaneous tumors are excised at a 45° angle with mapping, and light microscopy is used for subsequent identification of residual cancer. This method provides total histologic control of the surgical margins, and it achieves the lowest recurrence rate with maximal preservation of uninvolved tissue. Mohs surgery has become the treatment of choice for most skin cancers on the head and neck,[2] as well as for recurrent or histologically aggressive lesions.

History and nomenclature

As a medical student at the University of Wisconsin, Frederic E. Mohs initially developed his eponymous technique, at the time referred to as chemosurgery, by using a zinc chloride paste to fix tissue in vivo prior to surgical procedures. This chemosurgery fixed-tissue technique offered remarkably high cure rates, but it also had some drawbacks, including the following:

  • The application of zinc chloride paste on the skin cancer was uncomfortable for the patient.

  • Only one stage of Mohs surgery could usually be performed each day.

  • Zinc chloride paste caused tissue necrosis; therefore, immediate reconstruction was not possible until sloughing of any remaining fixed tissue was completed.

In 1953, during filming of the fixed-tissue technique for a basal cell carcinoma (BCC) of the eyelid, Mohs performed the last few layers without the zinc chloride fixative to speed up the process. The tangential frozen sections he obtained worked so well that Mohs continued this fresh-tissue technique for all eyelid carcinomas. In 1969, he reported a 5-year cure rate of 100% using the fresh-tissue technique to excise eyelid carcinomas. Wide acceptance of the fresh-tissue technique increased substantially after the publication of Tromovitch and Stegman's series in 1974 and Mohs' series in 1976.

Advantages of the fresh-tissue technique compared with the fixed-tissue technique of Mohs surgery include the following:

  • Avoidance of the pain caused by tissue fixation on the skin

  • Ability to perform multiple stages in one day

  • Ability to repair the defect immediately after tumor-free margins are achieved

The use of “chemo” in the name for the original technique was confusing to patients and physicians; as a result, the terms Mohs surgery and Mohs micrographic surgery came into existence. Currently, Mohs surgery, fresh-tissue technique, is the official name for this procedure, because the fixed-tissue technique is rarely used. The acronym MOHS, micrographically oriented histographic surgery, has also been proposed, but it has not achieved widespread recognition.

Changes in nomenclature have also occurred in the Mohs College as the terminology has evolved. The first annual meeting of the American College of Chemosurgery occurred in 1967. In 1986, the American College of Chemosurgery changed its name to the American College of Mohs Micrographic Surgery, because most surgeons were using the fresh-tissue technique rather than the fixed-tissue technique. To more accurately reflect the clinical practices of its members, its name was changed again in 1987 to the American College of Mohs Micrographic Surgery and Cutaneous Oncology (ACMMSCO). The current official name of the Mohs College has been condensed to the American College of Mohs Surgery (ACMS).


Before the 1980s, training in Mohs surgery was informal and without criteria. Currently, to become a member of ACMS, a physician must have successfully completed a 1- to 2-year postresidency fellowship that is invaluable in equipping trainees with competency in Mohs surgery, reconstructive surgery, and dermatopathology skills. Mohs surgery fellowships transitioned into American Council of Graduate Medical Education (ACGME) accredited fellowships, which were initially known as Procedural Dermatology, because these fellowships train fellows to perform not only Mohs surgery but other techniques as well. In 2014, the official name of the fellowship was changed to Micrographic Surgery and Dermatologic Oncology.[3]



Approach Considerations


Mohs surgery has become the treatment of choice for basal cell carcinomas (BCCs) and squamous cell carcinomas (SCCs) that are at high risk for local recurrence. Although most low-risk BCCs and SCCs can be successfully treated by using routine methods (eg, curettage and electrodesiccation, excisional surgery, cryosurgery), high-risk tumors are best treated with Mohs surgery (see the image below). For example, a superficial type of BCC on the arm is usually easily treated with routine methods due to its nonaggressive histologic growth pattern and nonfacial location.

Mohs surgery is generally indicated for the treatm Mohs surgery is generally indicated for the treatment of tumors in areas where a high risk of recurrence exists and cosmetic results are critical.

Appropriate use criteria for Mohs surgery were coreleased in 2012 by the American Academy of Dermatology, American College of Mohs Surgery, American Society for Dermatologic Surgery Association, and the American Society for Mohs Surgery.[4]  The criteria for the use of Mohs surgery are based on multiple factors, as described below. Tumors treated by Mohs surgery should ideally grow contiguously from a single focus of malignant cells, with histologic features amenable to frozen-section interpretation. More aggressive tumors, or tumors at higher risk for metastasis, may require adjunctive treatment, including lymph node dissection, radiation therapy, chemotherapy, or immunotherapy, even after histologically clear margins are achieved.

Basal Cell Carcinoma

All recurrent basal cell carcinoma (BCC) tumors or high-risk primary tumors with 1 or more of the following features are candidates for Mohs surgery:

  • Aggressive histologic growth pattern

  • Location in anatomic sites at which conventional treatment modalities have a higher potential risk of recurrence

  • Location at anatomic sites that require tissue conservation for optimal reconstruction

  • Other features

Aggressive histologic growth pattern

Aggressive histologic growth patterns include the following:

  • Sclerosing BCC (morpheaform BCC)

  • Infiltrating BCC

  • Metatypical BCC

  • Keratotic BCC

  • Collision tumors (BCC and SCC) or basosquamous cell carcinoma

  • Multicentric BCC

  • Clinically ill-defined micronodular BCC

  • Perineural and perivascular growth patterns

  • Field-fire BCC

  • Deep tissue or bone involvement

Anatomic sites with a higher potential risk of recurrence

The following areas have a higher risk of BCC recurrence with standard therapy (eg, curettage and electrodesiccation, excisional surgery, cryosurgery):

  • Periorbital and canthal regions

  • Central third of the face

  • Columella

  • Preauricular-tragal region

  • Postauricular sulcus region

  • Perioral region

  • Nasofacial sulcus and perinasal region

Anatomic sites requiring tissue conservation

Tissue conservation for optimal reconstruction is required in the following areas:

  • Nasal tip and alae

  • Lips (cutaneous and vermilion)

  • Eyelids

  • Auricular helix and canal

  • Hands and feet

  • Genitalia

  • Nail unit/periungal

  • Other

Other features

Other BCC features that are candidates for Mohs surgery include the following:

  • History of incomplete removal (recurrence or incomplete removal)

  • Rapid growth or aggressive clinical behavior

  • Tumors arising in a scar or ulcer

  • Large size (>1 cm on the face or >2 cm on the trunk and extremities)

  • Tumors in immunosuppressed patients

  • Tumors arising in patients with a history of previous radiation therapy

  • Tumors in patients younger than 40 years

  • Patients with basal cell nevus syndrome or xeroderma pigmentosum

  • Long-standing or neglected tumors

Recurrent BCC tumors

Mohs surgery is an excellent therapy for any recurrent tumor. BCCs tend to grow along the path of least resistance. When a tumor is excised and the wound is closed, the entire area of undermining provides a plane for extension of any incompletely excised tumor. Fibrosis from previous excisions and radiation can restrict the growth of a recurrent BCC and cause it to grow in unpredictable patterns. As a result, recurrent tumors tend to have much higher recurrence rates after conventional excision than primary tumors. Although Mohs surgery can result in the successful removal of recurrent tumors in 96% of the cases, conventional treatments achieve success only approximately 50% of the time.

Incompletely excised BCC tumors

Tumors with pathologically reported positive margins persist and recur in 33-43% of cases followed up for 2-5 years. Mohs surgery is an excellent way to treat these lesions, because it enables microscopic tumor extensions to be tracked precisely. Mohs surgery is indicated before recurrence occurs.

Aggressive BCC histologic subtypes

Tumors with an aggressive histologic nature (eg, micronodular, infiltrative, sclerosing/morpheaform, or keratinizing BCCs) have a higher rate of recurrence than nodular or superficial BCCs. Tumor removal with conventional margins is shown to result in incomplete removal at a rate of 6.4% for nodular BCCs and 3.6% for superficial BCCs. In contrast, the clinically ill-defined micronodular, infiltrative, and morpheaform tumors have much higher rates of incomplete removal of 18.6%, 26%, and 33.3%, respectively.

The high recurrence rates for these histologic subtypes with conventional excision reflect the degree of subclinical spread, which may not be adequately demonstrated on routine histopathologic examination. For example, morpheaform BCCs have subclinical extensions that average 7.2 mm beyond the clinically apparent tumor margins.

A field-fire BCC is a type of BCC tumor with discontinuous multicentric foci that may be a result of previous irradiation to the area, exposure to other carcinogens, or recurrence of the primary tumor at multiple foci. This type of tumor is best treated with Mohs surgery, because the margins of field-fire BCCs are difficult to determine clinically.

BCC tumor location

Cosmetically and functionally critical areas of the face that require tissue conservation at the time of surgery include the nasal ala, columella, junction of the ala with the nasolabial fold (ie, nasofacial sulcus), medial and lateral canthi, eyelids, preauricular and postauricular areas, philtrum, and vermilion borders of the lips. Other areas in which tissue conservation is important include the hands, feet, and anogenital areas.

Many of these anatomic areas also have unusually high recurrence rates for the skin cancers that arise within them. Recurrence rates for primary BCCs in these areas treated with conventional methods are as high as 43% on the lateral canthus, 33% on the superior orbital rim and brow, 24% on the ear, and 19% on the nose. In contrast, only 0.5% of primary BCCs located on the neck, trunk, and extremities treated with conventional methods recur within 5 years. Certain areas on the scalp also have high recurrence rates.

BCC tumor size

Mohs surgery is the best treatment for a maximal rate of cure for tumors larger than 0.6-1 cm on the face and those larger than 2 cm on the trunk and extremities. The success rates in treating BCC with conventional surgical methods decrease with increasing tumor size. After treatment with standard modalities, recurrence occurs in 3.2% of patients with primary BCCs smaller than 6 mm, 5.2-8% of those with 6-9–mm tumors, and 9% of patients with BCCs larger than 9 mm.

BCC treatment and recurrence rates

Table 1 summarizes the types of treatment for BCCs based on the tumor features. Table 2 outlines BCC recurrence rates based on the type of treatment administered.

Table 1. Treatment of Basal Cell Carcinoma Based on Tumor Features (Open Table in a new window)

Feature of Tumor

Mohs Surgery

Excision, Electrodesiccation and Curettage, Cryosurgery, and Radiation Therapy

Primary or recurrent

Recurrent or incompletely excised



High risk; on ear, digits, genitalia, or central part of face

Low risk; on trunk and extremities

Histologic finding

Aggressive growth pattern: morpheaform, infiltrating, keratotic, perineural or perivascular invasion

Nodular, superficial


>0.6-1 cm on face, >2 cm elsewhere

< 0.6-1 cm on face, < 2 cm elsewhere

Clinical nature

Ill-defined borders, multicentric, radiation, genetic syndrome with multiple tumors

Well-defined borders

Table 2. Basal Cell Carcinoma Recurrence Rates by Treatment (Open Table in a new window)


Primary Tumor, %

Recurrent Tumor, %

Mohs surgery



Surgical excision









Electrodesiccation and curettage



* Less than 5 years; no statistics for 5-year follow-up.


Squamous Cell Carcinoma

Squamous cell carcinoma (SCC) is the second most common skin cancer in white individuals and the second most common tumor treated with Mohs surgery. Annually, cutaneous SCCs are responsible for 2000-5000 deaths in the United States.

Most cutaneous SCCs are at low risk for recurrence or metastasis. Small, well-differentiated, primary SCCs on actinically damaged skin have a metastatic rate of 1% or less and are easily treated with standard modalities (eg, curettage and electrodesiccation, excisional surgery, cryosurgery). However, a subset of these tumors may be aggressive and present more of a challenge to the surgeon because of their increased ability to metastasize.[5, 6]

The metastatic rate of SCC varies depending on the following tumor features:

  • Size

  • Depth of invasion

  • Degree of histologic differentiation

  • Location

  • Presence of perineural or perivascular involvement

  • Underlying medical conditions (eg, immunosuppression)

  • Metastasis most commonly occurs after previous unsuccessful treatment. Therefore, appropriate initial therapy of SCCs is critical.

Mohs surgery is the treatment of choice for high-risk SCCs; this procedure has a local recurrence rate of 3% compared with 13% for all non–Mohs surgery modalities. Recurrent tumors have a 25-45% metastatic rate, depending on anatomic site. The 5-year survival rate for metastatic SCC is only 25%.

The recognition and successful treatment of high-risk tumors (SCCs at high risk for local recurrence or metastasis) is important for patient survival. SCCs that meet the following high-risk criteria are best treated with Mohs surgery:

  • Large size (>2 cm)

  • Depth of invasion (>4 mm)

  • Recurrent or incompletely excised tumors

  • Histologic subtype, including undifferentiated, poorly differentiated, acantholytic (pseudoglandular)

  • Perineural or perivascular invasion

  • Rapid growth

  • Long duration

  • Tumors in immunosuppressed patients

  • Radiation-induced lesions

  • Certain genodermatoses (inherited skin conditions)

The following anatomic sites are also at high risk for local recurrence or metastasis:

  • Scalp

  • Temple

  • Periorbital and canthal region

  • Central third of the face

  • Columella

  • Lips (cutaneous and mucosal areas)

  • Other mucous membranes

  • Ears

  • Preauricular-tragal region

  • Postauricular sulcus

  • Lower extremities

  • Nail bed and matrix

  • Genitalia

In addition, tumors that arise in certain areas, such as the following, are at high risk for local recurrence or metastasis:

  • Previously irradiated skin

  • Thermal and radiation scars

  • Chronic sinus tracts and ulcers

  • Chronic osteomyelitis

  • Lichen sclerosis et atrophicus

  • Discoid lupus erythematosus

Size and depth

The size of the tumor and the depth of the SCC tumor invasion are the 2 most important prognostic factors. Most metastasizing cutaneous SCCs are reported to be larger than 2 cm in diameter. Tumor invasion deeper than 4 mm (Clark level IV-V), have higher metastatic and recurrence rates than those that invade with a depth of less than 4 mm (Clark level I-III).

Rowe et al reported that SCCs with a depth less than 4 mm have a local recurrence rate of 5.3% and a metastatic rate of 6.7%.[7] Lesions deeper than 4 mm have a local recurrence rate of 17.2% and a metastatic rate of 30.3%.[7]

Recurrent tumors

As noted above, recurrent tumors have a metastatic rate of 25-45%, depending on their anatomic site. Because metastases occur most commonly after previous unsuccessful treatment, Mohs surgery is the treatment of choice for recurrent tumors and has a reported local recurrence rate of 10%, compared with 23% with standard excision.

Histologic subtype

Most SCCs are small, are well differentiated, and arise on actinically damaged skin. These SCCs are nonaggressive and have a metastatic rate of less than 1%. Poorly differentiated histologic features are seen in only 19.1% of all cutaneous SCCs, but they account for 51% of SCCs that metastasize. These tumors have more than double the recurrence rate and triple the metastatic rate of well and moderately differentiated SCCs. Adenoid (eg, pseudoglandular, acantholytic) SCCs also have an increased rate of metastases.

Anatomic site

Mohs surgery is indicated for SCCs that arise in locations at high risk for recurrence or metastases, particularly the ear and mucous membranes—sites that are consistently reported to have a higher risk of metastases. Metastatic incidence rates of 11% are reported for SCCs on the ear and 13.7% on the lips. SCCs of the penis, scrotum, and anus have higher metastatic rates than SCC of the lips. SCCs within a burn scar, those within a site of previous irradiation, and those induced by chronic osteomyelitis have metastatic incidence rates of 18%, 20%, and 31%, respectively.

Other areas at high risk include the periorbital and canthal areas, central third of the face, columella, lower extremities, temple, scalp, and nail bed and matrix.

Perineural or perivascular invasion

SCCs with perineural invasion are at greater risk for recurrence, lymph node metastases, and distant metastases. The more aggressive SCCs (eg, recurrent SCCs, larger SCCs) often show perineural invasion. Perineural invasion is reported in 64% of tumors with a diameter of 2.5 cm or larger, but only in 11% of tumors with a diameter of 2.5 cm or less involve perineural invasion.[7]

Tumors with perineural invasion have a local recurrence rate of 47.2% and a metastatic rate of 47.3%.[7] With perineural invasion, the local recurrence rate is almost 50% after standard excision followed by radiation. Radiation therapy alone is reported to result in an 80% recurrence rate.[7]

The treatment of choice for SCC with perineural invasion of larger nerves appears to be Mohs surgery followed by radiation therapy. Three studies of this combined treatment involving a total of 32 patients demonstrated a recurrence rate of 6%. However, the cases in these series were followed up for less than 3 years.

Rapid growth

SCCs that visibly enlarge between the time of diagnosis and treatment are especially aggressive. The metastatic rate of rapidly growing tumors on the ears and eyelids is 3 times that of slower growing SCCs.

Other Tumors

Mohs surgery is applied to many different types of tumors in different clinical settings. Although its use and application is straightforward in most instances, Mohs surgery of certain tumors may be controversial because of various factors (eg, multifocality, discontinuous growth patterns, in-transit metastasis, inherent disadvantages of frozen sections vs permanent sections).

The following discussion focuses on the less controversial additional indications for Mohs surgery.

Verrucous carcinoma

Verrucous carcinoma[8, 9] is a distinct clinicopathologic variant of SCC that most commonly affects the mouth (eg, oral florid papillomatosis), foot (eg, epithelioma cuniculatum), and penis (eg, giant condyloma of Buschke-Löwenstein). Although verrucous carcinoma rarely metastasizes, it penetrates deeply, invading contiguous structures. Tumors treated with surgical excision have a cure rate of 80%; however, the reported cure rate with Mohs surgery approaches 98%.


Keratoacanthomas (KAs)[10, 11, 12, 13, 14, 15] are cutaneous tumors that histologically resemble SCCs, but they have a tendency to spontaneously involute. These tumors are reported to have a recurrence rate of 8%. Similar to SCCs, recurrent KAs are often histologically aggressive and can metastasize. Although several reports of metastatic KAs exist, it is debatable whether the tumors were KAs or misdiagnosed SCCs or whether KAs actually are a variant of SCC.

KAs can cause extensive local destruction, particularly if they arise on the eyelid or nose, before regression occurs. This extensive local destruction is especially problematic with some KA variants (eg, giant KA, KA centrifugum marginatum, subungual KA). For example, giant KAs can become larger than 9 cm and have a predilection for the nose and dorsum of the hands. It is not possible to predict which KAs will progress to the giant variant by either clinical or histologic means.

Mohs surgery is the ideal treatment for KAs that are recurrent or near vital structures (where tissue conservation is warranted) because of the unpredictability of spontaneous regression and the potentially destructive nature of these tumors.

Extramammary Paget disease

Extramammary Paget disease (EMP)[16, 17, 18, 19, 20, 21, 22, 23] begins as an erythematous, eczematoid, slowly spreading plaque that usually affects sites with a high density of apocrine glands (eg, vulvar, perineal, perianal regions). The penis, axillae, umbilicus, eyelids, and external auditory meatus are less common sites.

The histogenesis of EMP remains controversial. Although it is usually a primary tumor, EMP may be secondary to an adnexal or visceral carcinoma. Approximately 25% of cases have an underlying cutaneous adnexal carcinoma, mostly of the apocrine type, but the carcinoma is sometimes derived from eccrine, periurethral, perianal, or Bartholin glands. In addition, 10-15% of patients have an internal carcinoma that appears to be of etiologic significance. In these cases, the epidermal pagetoid cells are thought to represent epidermotropic metastases. The prognosis in EMP cases associated with an underlying malignancy is poor, with a mortality rate of 50% or higher.

Local recurrence of EMP is common because of histologic extension beyond the clinically apparent extent of the tumor. The recurrence rate with standard excision is 31-61%, whereas Mohs surgery has recurrence rates of 23-33%. Thus, Mohs surgery is advantageous for the treatment of EMP because of its lower recurrence rate as well as its tissue-sparing capability in critical areas, such as the anogenital region.

The high rate of recurrence despite visualization of the entire tumor margin is thought to be due to the multifocal growth pattern of this tumor. Some surgeons use topical fluorouracil before performing Mohs excision, because this agent causes marked inflammation and erythema of the involved skin, which better delineates the margins of the tumor. A rapid carcinoembryonic antigen (CEA) stain is used to distinguish between artifactual vacuoles and pagetoid cells, which have similar appearances on routine hematoxylin and eosin staining.

Microcystic adnexal carcinoma

Microcystic adnexal carcinoma (MAC),[24, 25, 26, 27, 28, 29] also referred to as sclerosing sweat duct carcinoma, is a more recently described, uncommon, malignant eccrine tumor that is known for its aggressive local invasion of tissue. MAC rarely metastasizes; however, it usually involves deep soft tissue and dermis and has a propensity for perineural invasion.

At histologic examination, the superficial component is made up of numerous keratinous cysts, small islands and strands of basaloid cells, and squamous epithelium with variable ductal differentiation. The deeper component has smaller nests and strands of cells in a dense, hyalinized stroma. When superficial biopsy is performed, the histologic features of a MAC can be mistaken for those of tumors, such as basal cell carcinoma (BCC), SCC, syringoma, or desmoplastic trichoepithelioma.

Clinically, MAC most often appears as a solitary, flesh-colored, indurated plaque on the face of middle-aged women. Because of its nondescript appearance and clinical and histologic resemblance to other benign and malignant neoplasms, MAC is incorrectly diagnosed in 30% of the cases.

Mohs surgery should be strongly considered as a first-line modality for the treatment of MAC, because the tumor grows contiguously and is well suited for removal using this procedure. Local recurrences after traditional excisional surgery approach 47%. In addition, standard excision is more likely to lead to a larger defect than Mohs surgery. However, the relative rarity of MAC tumors has rendered comparative trials regarding treatment difficult.

A retrospective study involving 48 cases with a mean follow-up time of 3.2 years showed that Mohs surgery is clearly advantageous compared with standard excision with respect to the number of procedures required for cure.[25] Of 23 patients treated with standard excision at the onset, 7 (30%) patients required at least 1 other procedure compared to none (0%) of 22 patients treated with Mohs surgery.

Dermatofibrosarcoma protuberans

Dermatofibrosarcoma protuberans (DFSP)[30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44] is an uncommon, slow-growing, locally aggressive tumor with a marked tendency for local recurrence, but it rarely metastasizes. Although DFSP is traditionally thought to be of fibrohistiocytic lineage, the histogenesis is in dispute.

Mohs surgery is well established for the treatment of primary and recurrent DFSPs and is suggested as the treatment of choice for these tumors. Wide surgical excision with a margin of at least 3 cm down to the fascia is recommended, although multiple recurrences are frequently reported. Dedifferentiation of the tumors into high-grade sarcomas, with a subsequent increased risk of metastasis, may result from multiple recurrences after inadequate initial treatment.

In a study of patients with DFSP treated with modified Mohs surgery, Serra-Guillén et al found that the mean number of surgery stages needed was 1.47 and the mean minimum margin required was 1.23 cm, to achieve tumor clearance. However, head and neck tumors had greater subclinical extension, with significantly more Mohs surgery stages and a significantly wider margin needed for these.[45]

One review of the world literature revealed a recurrence rate of 1.6% when Mohs surgery was used for the treatment of DFSP versus a 20% recurrence rate with wide excision.[35] Another study showed that if standard excisions are performed, margins of 1 cm around the primary tumor left microscopic residual tumor in 70.7% of cases; margins of 2 cm, 39.7%; margins of 3 cm, 15.5%; and margins of 5 cm, 5.2%.[42] Some tumors were not completely excised with 10-cm margins.[42]

During Mohs surgery, delineating the true borders at the periphery of the specimen can occasionally be difficult, because sparse malignant cells may resemble normal fibroblasts. The immunostain CD34 is selectively expressed by DFSP, and its use should improve the ability to differentiate the neoplastic cells from fibroblasts. CD34 is also used to detect those cells masked by inflammation.[46, 47] At times, Mohs surgery may be followed by excision of a conservative additional margin for permanent section evaluation to ensure the removal of all involved tissue to the greatest extent possible.

Sebaceous carcinoma

Sebaceous carcinoma[48, 49, 50] is an uncommon aggressive malignant tumor derived from the adnexal epithelium of the sebaceous glands. Sebaceous carcinomas can arise in ocular or extraocular sites, and they have such diverse clinical presentations and histologic growth patterns that the diagnosis is often delayed for months to years.

Ocular and extraocular sebaceous carcinomas have high rates of recurrence (33-34%) and distant metastases (30-32%). The high tumor recurrence rate may result from misdiagnosis that results in undertreatment. Sebaceous carcinomas may have multicentric, noncontiguous foci and pagetoid or intraepithelial spread that result in incomplete excision of the tumors with either traditional methods or Mohs surgery.

Several early reports demonstrated success with Mohs surgery, and some authors advocate its use as the treatment of choice for sebaceous carcinomas that do not involve the orbit, regional nodes, or distant organs. Mohs surgery offers the potential for maximal tissue conservation and the highest cure rate. However, use of paraffin-embedded sections, oil red O staining of frozen sections, and other techniques assist in determining tumor-free margins. Careful clinical and radiologic follow-up is recommended.

Atypical fibroxanthoma

Atypical fibroxanthoma[51] is a low-grade malignancy that is thought to be a superficial variant of a malignant fibrous histiocytoma. This tumor is most often seen in actinically damaged skin on the head and neck of elderly patients, but sporadic cases are reported on the trunk and extremities.

Conventional surgery is considered the mainstay of therapy for atypical fibroxanthomas, because recurrence rates are typically less than 10-16%. These tumors are also successfully treated with Mohs surgery, with the potential for lower rates of recurrence in addition to maximal tissue conservation. To the principal author's knowledge, owing to the low numbers of cases, no studies have been performed to adequately compare the effectiveness of Mohs surgery versus conventional excision.

Malignant melanoma

The issue of treating malignant melanoma[52, 53, 54] with Mohs surgery is controversial. In frozen sections of severely sun-damaged skin, even clinically uninvolved skin may have atypical keratinocytes, a loss of normal epidermal architecture, and atypical melanocytes that may simulate in situ melanoma and result in false-positive margins. Because of these observations, some authors advocate the use of paraffin-embedded sections or special stains.

Several immunostains are available for melanoma that can be used on frozen sections. These include HMB-45, S-100, Mart-5, and Melan-A (A-103). However, clinicians who use frozen sections alone cite impressive results with Mohs surgery and achieve survival and metastatic rates comparable to those of wide surgical excision. In addition, these authors report achieving narrower excision margins without a higher risk of local recurrence due to incomplete excision.

The advantage of the Mohs technique is that 100% of the surgical margin of the specimen, including the periphery and undersurface, is examined. Moreover, the maximal amount of normal tissue is conserved with the Mohs method, which is of particular value in treating tumors on the face or in other critical areas. In contrast, only 0.01% of the margin is sampled when a standard surgical pathologic technique is used.

Lentigo maligna and lentigo maligna melanoma

A literature review by Sharma et al indicated that, despite controversy over its use in the treatment of patients with lentigo maligna (LM) or lentigo maligna melanoma (LMM), Mohs surgery can effectively be employed in such cases. The investigators pointed to concerns, as mentioned above, that frozen sections are not an optimal means of distinguishing atypical melanocytes. Their report, however, revealed an overall recurrence rate of just 1.35% following Mohs surgery for LM or LMM (follow-up periods being 1 month to 5 years). This compared favorably with other treatments for these conditions.[55]

Unusual Tumors

Mohs surgery is used alone or as an integral part of an overall treatment approach for many other unusual cutaneous neoplasms. However, the small number of such cases precludes any definitive conclusions about the utility of this technique.

Mohs surgery may be used to treat the following unusual tumors:

  • Adenoid cystic carcinoma of the skin[56]

  • Angioendothelioma

  • Angiosarcoma[57]

  • Apocrine carcinoma of the skin

  • Certain aggressive locally recurrent benign tumors

  • Desmoplastic trichilemmoma[58]

  • Eccrine adenocarcinoma[22]

  • Erosive adenomatosis of the nipple[59]

  • Erythroplasia of Queyrat

  • Glandular carcinoma

  • Granular cell tumor

  • Hemangioendothelioma

  • Hemangiosarcoma

  • Leiomyosarcoma[60, 61, 62]

  • Liposarcoma

  • Lymphoepitheliomalike carcinoma of the skin

  • Malignant cylindroma

  • Malignant fibrous histiocytoma[63, 64]

  • Malignant schwannoma

  • Neuroendocrine carcinoma of the skin (Merkel cell carcinoma)

  • Oral and central facial paranasal sinus neoplasms

  • Pilomatrix carcinoma[65]

  • Other tumors that are histologically contiguous with locally aggressive growth

Disadvantages of Mohs Surgery

Disadvantages of Mohs surgery include the following:

  • The procedure may become tedious and prolonged for the patient; especially if the case is difficult or complex.

  • An inability to remove a large or difficult tumor in one day may preclude immediate reconstruction after complete excision.

  • The procedure requires a specially trained dermatologist and ancillary personnel.

  • Multiple injections of local anesthetic can cause patient discomfort.

Mohs surgery is usually an outpatient procedure and takes 3 hours to complete, on average. However, some very complex cases may take an entire day or longer, and additional time may also be required when tumors are more extensive than usual. Furthermore, if a complex case requires reconstruction by a different specialist, the resulting wound may require delayed closure (ie, a separate surgical procedure, perhaps on another day, may be necessary to repair the defect).

Mohs surgery is cost effective owing to its high cure rate and because it is usually performed with local anesthesia on an outpatient basis. The cost of Mohs surgery compares favorably with that of excision with frozen-section interpretation, but Mohs surgery results in superior cure rates owing to the complete review of the surgical margin with horizontally oriented tissue processing, and it requires only one specialized provider to serve as the surgical oncologist, pathologist, and reconstructive surgeon. However, if Mohs surgery is used in skin cancers that could adequately be treated with routine modalities (eg, curettage and desiccation), it no longer remains cost effective.

Limited accessibility of Mohs surgery may be a problem in some communities due to the need for a dermatologist with specialized training and for ancillary support personnel trained in performing the procedure.

Limitations of Mohs Surgery

Mohs surgery is most successful in treating certain cutaneous neoplasms, and it can be used alone or in a multidisciplinary approach to achieve the highest possible cure rate for a variety of difficult-to-treat tumors. However, limitations of Mohs surgery may include the following:

  • Noncontiguous tumors and/or disconnected foci in tumors may result in recurrence.

  • Adjunctive therapy may be necessary to ensure cure.

  • The extent of the tumor may be too great to be amenable to surgery.

Mohs surgery is indicated for the treatment of skin tumors that primarily spread by direct extension (ie, tumors that grow contiguously). This procedure would not be appropriate for tumors that have satellitosis, a multicentric origin, or skip areas. However, routine surgical excision of such tumors also fails, often at the expense of excessive tissue sacrifice.

Mohs surgery may also be limited by the extent of the tumor. This procedure is indicated for special situations, such as tumors that are deeply penetrating or that have perineural invasion. If the tumor is so deeply invasive that it involves bone and/or vital structures, a multidisciplinary approach is indicated. For example, tumors that invade bone may need to be cleared peripherally using Mohs surgery; an additional specialist, such as an otolaryngologist and/or head and neck surgeon, may be consulted to treat the deep component of the tumor.

Occasionally, the morbidity of a surgical approach for a tumor outweighs the benefit. In such cases, other therapeutic options, such as radiation therapy, should be considered.

Preoperative Planning

Preoperative surgical planning is important to ensure that the procedure is as safe as possible. The Mohs surgeon thoroughly investigates and evaluates the patient's general health, history (eg, medications, drug allergies, and social and occupational situation), and previous treatment (prior operations or hospitalizations), as well as the gross appearance and histopathologic features of the skin tumor.

Patient considerations

During the Mohs surgical consultation, the surgeon should specifically ask the patient about any conditions that may cause a problem during or after surgery (eg, underlying diabetes mellitus, cardiovascular or pulmonary compromise, history of prolonged bleeding, or tendency for keloid and/or scar formation). The surgeon also thoroughly explains the surgical technique to the patient, discusses the advantages and disadvantages of Mohs surgery compared with other therapeutic options, and reviews possible complications of the surgery. Wound care and reconstructive options are also reviewed.

Other preoperative considerations should be addressed, including alcohol and tobacco cessation; food, medications, and attire on the day of surgery, as well as postoperative issues. Patients should not drink alcohol 24 hours prior to the procedure or 48 hours after the procedure to reduce the risk of bleeding. Cigarette smokers should be advised to decrease smoking to the greatest degree possible for 1 week before and 1 week after surgery to decrease the risk of poor wound healing.

All patients should eat breakfast prior to the Mohs procedure as well as bring a snack, because the procedure is lengthy and may deplete the patient's energy and alter their blood sugar level. Instruct patients to wear casual, warm, layered clothing with buttons, rather than pullover clothing. Remind patients to take all their prescribed medications at the regular time and to bring extra medication in case the surgery is longer than anticipated. Patients should also make arrangements to be escorted home after the surgery if the surgery involves an area close to the eye or if it may prevent them from walking or driving.

For patient education resources, see Cancer Center as well as Skin Cancer and Skin Biopsy.

Clotting parameters

In Mohs surgery, flaps and grafts are occasionally needed to repair resulting defects. If a patient has a bleeding diathesis or has been taking aspirin, warfarin, antiplatelet medications, or nonsteroidal anti-inflammatory drugs, the flap or graft survival could be compromised. Additionally, these patients are at higher risk for hematomas and infection.

In recent years, there has been a trend to continue anticoagulants and antiplatelet medications during surgery, because the risk of a severe thromboembolic event outweighs the risk of acute bleeding. It is the principal author’s practice to coordinate with other care providers to keep the patient's international normalized ratio (INR) to 3 or less, but within the therapeutic window. Most hemostasis can be safely obtained by using electrocautery or electrodesiccation and a pressure bandage.

Prophylactic medications

During the surgical consultation, the Mohs surgeon also determines whether prophylactic antibiotics are necessary. To prevent the development of bacterial endocarditis in patients with high- or moderate-risk cardiac conditions, the American Heart Association (AHA) recommends the use of prophylactic antibiotics for dental and/or oral and/or upper respiratory tract procedures, as well as some genitourinary and/or gastrointestinal procedures.[66] However, Mohs surgery does not usually fall into any of these categories, and most authorities do not advocate the use of prophylactic antibiotics for Mohs surgery (or other lengthy surgical procedures) even for patients with a history of prostheses (valves or joints), nonphysiologic heart murmurs or valvular disease, or mitral valve prolapse.

Prophylactic antibiotics are recommended when the surgical site is considered high risk for surgical infection; these locations include the oral mucosa, genitalia, and the lower extremities below the knee.[67] Consideration is also given to patients who are diabetic or immunosuppressed. In addition, if a graft or flap is used to close the wound and antibiotics are not given prophylactically, postprocedure antibiotics are often given for 1 week. Due to an increase in community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) in recent years, patients who have had CA-MRSA infections or who are chronic carriers are also recommended to have prophylactic antibiotics and/or a 1-week course of postoperative antibiotics.

The most commonly used perioperative prophylactic antibiotics include dicloxacillin and cephalexin (2 g PO 1 h prior to surgery). For penicillin-allergic patients, the principal author uses either clindamycin (600 mg 1 h prior to surgery) or azithromycin (500 mg PO 1 h prior to surgery). For postoperative antibiotic agents, the principal author prefers cephalexin or azithromycin (for penicillin-allergic patients). For special situations such as CA-MRSA, the principal author uses doxycycline or sulfamethoxazole; for exposed cartilage, ciprofloxacin is used.

Allergic drug reactions

Medication allergies are common in patients. Aside from allergies to oral antibiotics, many patients are allergic to topical antibiotics, with the most common topical offenders including bacitracin/polymyxin B sulfate (eg, Polysporin), neomycin/gramicidin/polymyxin (eg, Neosporin), and bacitracin. For patients who are allergic to any of these topical antibiotics, use an ointment base (eg, Aquaphor), petrolatum, or mupirocin (eg, Bactroban).

Contraindications for epinephrine

In patients taking nonselective beta-blockers or those with a history of severe hypertension, heart failure, or dysrhythmias, the principal author generally prefers to use plain lidocaine without epinephrine for local anesthesia.

Electrosurgery for hemostasis in select patients

For patients with pacemakers and implantable cardioverter-defibrillators (ICDs), the literature shows that it is safest to utilize electrocoagulation using bipolar forceps or a hand-held heat cautery device.[68, 69] However, commonly practiced precautions such as applying short bursts (< 5 seconds), using minimal power, and avoiding use of electrosurgery around the implanted device also have low rates of complications.

For patients with deep brain stimulators (DBS), use handheld heat cautery, or ask the patient to obtain a remote handheld controller to turn off the unit during cautery.


For all patients, the size, location, and histologic subtype of the tumor dictate the type of resources required. Anticipate the need to consult with colleagues from other surgical or medical specialties when appropriate, such as when the Mohs surgeon anticipates an extensive or high-risk defect that requires specialized repair or the use of an additional therapeutic modality. If interdisciplinary cooperation is necessary, consultation with the appropriate specialist should be initiated prior to the day of the Mohs surgery, and care should be coordinated between the Mohs surgeon and the other specialists.



Approach Considerations

The cornerstone of Mohs surgery is based on the observation that cutaneous neoplasms often grow contiguously with unpredictable, lengthy, rootlike extensions that can spread deeply or laterally from the clinically apparent lesion. When the tangentially oriented Mohs surgery technique is used to examine surgical margins, almost 100% of tumor margins are microscopically examined, as opposed to less than 1% with traditional histologic methods.

A study by Nätterdahl et al of patients who underwent Mohs surgery for BCC indicated that risk factors for complicated Mohs surgery (defined in the study as Mohs surgery requiring three or more stages) include older age, previous tumor treatment with cryotherapy, and more than one prior surgery. The odds ratios for these factors were 1.02, 2.3, and 3.4, respectively.[70]

Traditional tumor excision methods

Traditional methods of tumor excision involve the removal of the clinically evident tumor along with an additional margin of normal-appearing tissue. The additional margin is removed because malignant extensions are microscopic; the malignant extensions cannot be clinically visualized or palpated.

After the tumor is excised, conventional microscopic processing is used to assess the margins of the specimen for residual tumor. Representative vertical sections may be obtained at 2- to 4-mm intervals throughout the specimen by using the bread-loaf method and in each of 4 quadrants by using the quadrant method. When the tissue sample is microscopically seen to be tumor free, the entire margin from which the sample was obtained is also assumed to be tumor free.

However, a tumor that is determined to have clear margins with the use of these methods may actually have fingerlike extensions in the unexamined intervals, because less than 1% of the interface between the specimen and the patient is actually examined histologically. The failure of these methods to permit consistent identification of residual tumor explains the incidence of local recurrence despite the finding of margins that appear to be tumor free (see the image below).

The conventional bread-loaf technique for checking The conventional bread-loaf technique for checking tissue margins by using vertical sections. Less than 1% of the margin is evaluated, as compared with almost 100% of the margin with the Mohs surgical technique. As illustrated here, residual tumor may not be found and may recur.

Various empiric approaches to surgical removal of skin cancers are recommended on the basis of studies of tumor size, type, and histologic subtype; however, these approaches are not always sufficient for complete tumor removal. For example, although 2- to 3-mm margins are often recommended for the treatment of small nodular basal cell carcinomas (BCCs), such narrow margins are not always adequate.

Although Burg et al showed that 5-mm margins are necessary to ensure adequate excision of clinically well-defined BCCs, and 9- to 10-mm margins are necessary for complete removal of morpheaform BCCs and tumors larger than 2 cm in diameter,[71] this approach assumes that tumor growth is symmetrical in all directions, which is frequently not the case, especially with recurrent, large, or infiltrative tumors. Furthermore, wider surgical margins that lead to reproducibly high cure rates may leave functionally or cosmetically unacceptable results, particularly on the face or scalp, which are common sites of skin cancer.

Confocal laser scanning microscopy

The epidermis and part of the dermis can be visualized using a confocal scanning microscope, based on different refractive indices of various structures in the skin. The US Food and Drug Administration has approved these microscopes, and clinical studies for their use in Mohs surgery are under way.

Special stains

In recent years, immunostaining has facilitated the successful removal of a number of cutaneous malignancies. Selective labeling of malignant cells can help to more clearly delineate tumors that may be masked by inflammation; this is helpful when a tumor presents with subtle or nonspecific histologic features.

Examples of immunostaining techniques include antikeratin for BCCs and squamous cell carcinomas (SCCs), anti-CD34 for dermatofibrosarcoma, MART-1 for malignant melanoma, and anti–carcinoembryonic antigen (anti-CEA) for extramammary Paget disease (EMP). However, the disadvantages and limitations of incorporating immunohistochemistry into a Mohs surgery practice include the additional processing time and cost involved, as well as more time-consuming interpretations.

Nevertheless, progress continues to be made in an effort to make immunostains more cost effective. For example, Kimyai-Asadi and colleagues reported a 20-minute rapid MART-1 immunostaining protocol that has significantly improved the efficiency in the workflow.[52] As research and development advance, the use of immunohistochemistry in Mohs surgery is expected to become a more widely used technique.

Fresh-Tissue Technique

Although the process of performing the fresh-tissue technique of Mohs surgery varies according to individual practices among physicians, the basic procedure is similar, as follows:

  • Step 1: The surgeon begins by outlining the tumor with a marking pen prior to injecting the area with local anesthesia (0.5-2% lidocaine with epinephrine 1:100,000 or 1:200,000), because the anesthesia may distort anatomic landmarks and the tumor's true extent.

  • Step 2: After waiting several minutes for maximal anesthesia and vasoconstriction, some surgeons use a curette to debulk the tumor, which tends to be softer than the surrounding normal skin, to better delineate its extent; however, this method may be less effective with morpheaform basal cell carcinomas (BCCs) or other nonfriable tumors.

  • Step 3: To allow precise orientation of the specimen, some surgeons tattoo the tumor with a substance such as methylene blue, whereas others use hatch marks, sutures, staples, or superficial scalpel incisions at the periphery of the specimen.

  • Step 4: The tissue is then excised with the scalpel angled 45° to the skin to bevel the edge to facilitate histologic processing; the excision is continued circumferentially around the tumor at a 45° angle and under the skin parallel to the surface so that the deep margin is excised horizontally.

  • Step 5: Hemostasis is achieved by using spot electrodesiccation, suture ligatures, oxidized cellulose (eg, Surgicel, Oxycel), pressure, or other methods.

  • Step 6: A 2-dimensional map of the patient's skin defect is drawn, incorporating the hatch marks, sutures, staples, or incisions that were used to orient the specimen.

  • Step 7: The tissue is divided along the tattooed or scored lines and inverted (dermis turned up); then, the edges of the specimen are color-coded with tissue dyes (see examples in the images below).

    A Mohs surgery specimen is carefully separated int A Mohs surgery specimen is carefully separated into 4 quadrants.
    Each quadrant of a specimen undergoing Mohs surger Each quadrant of a specimen undergoing Mohs surgery is marked with 2 different colored dyes.
  • Step 8: The histotechnician mounts the tissue as it is presented, flattening the undersurface in an even horizontal plane; cuts 5- to 7-µm horizontal frozen sections of each tissue specimen with a cryostat (see the images below); and places the specimens on slides. (By compressing each saucerized piece of tissue and sectioning the specimen horizontally from the deep margin upward, the entire undersurface and epidermal margin of the excised specimen is theoretically processed. Histologic preparation for microscopic examination in Mohs surgery requires skill and practice. Minor variations in technique may exist.)

    Marked tissue undergoing Mohs surgical technique i Marked tissue undergoing Mohs surgical technique is embedded into a chuck for the cryostat.
    A Mohs surgery tissue specimen is cut into thin se A Mohs surgery tissue specimen is cut into thin sections.
  • Step 9: The slides are stained (usually with hematoxylin-eosin or toluidine blue), and the Mohs surgeon, who also serves as the pathologist, interprets the results (see the following images).

    Mohs surgery sections are stained with hematoxylin Mohs surgery sections are stained with hematoxylin and eosin and placed on slides.
    Mohs surgery sections are stained with hematoxylin Mohs surgery sections are stained with hematoxylin and eosin and placed on slides.
  • Step 10: Any residual neoplasm is marked on the map in red ink (see the image below); the surgeon can then precisely remove additional tissue where residual tumor is identified—in this manner, uninvolved tissue is preserved, because only the areas with residual tumor are sequentially removed.

    Residual tumors are marked on a map. Residual tumors are marked on a map.
  • Step 11: With the fresh-tissue technique, the resulting defect can be reconstructed immediately (discussed below).

Depending on the size and location of the resulting wound, the surgeon then chooses the most appropriate reconstructive repair to achieve the best functional and cosmetic outcome. These reconstruction techniques include primary closure, adjacent tissue transfer (flap), skin graft, and a combination of the previous techniques.

Many post-Mohs technique defects can be repaired in a linear fashion via primary closure. However, larger defects or anatomically difficult locations warrant repair with a full-thickness skin graft (FTSG) or flaps. For example, due to limited blood perfusion, tightness, and fragility of the overlying skin, FTSG is suggested to be a safe reconstructive option for lower-extremity defects after Mohs surgery.[72] An experienced, fellowship-trained Mohs surgeon has extensive experience with all these types of reconstructive surgery techniques.

Coordinating the roles of the dermatologist, pathologist, cutaneous and/or oncologic surgeon, and reconstructive surgeon ensures the least amount of error when the histopathologic and clinical findings of each patient are correlated.

The following image demonstrates an example of the fresh-frozen technique of Mohs surgery.

An illustrated example of the Mohs surgical techni An illustrated example of the Mohs surgical technique.

Fixed-Tissue Technique

The fixed- and fresh-tissue Mohs surgery techniques are similar. However, with the fixed-tissue technique, the tissue fixation is accomplished before excision, thereby eliminating the need for anesthesia and creating a blood-free surgical field.

Although the fixed-tissue technique is infrequently used, some surgeons find it helpful in certain circumstances. For example, the blood-free field may be useful for penile carcinomas because of the associated vascularity of the tissue.

The fixed-tissue technique consists of the following:

  • Step 1: The tumor is debulked with a curette, and dichloroacetic acid is applied to increase the penetration of the zinc chloride paste and to facilitate hemostasis. (The dichloroacetic acid is a keratolytic agent; therefore, heavily keratinized areas require the application of more of the agent, whereas ulcerated surfaces do not necessarily require application of the acid.)

  • Step 2: A layer of zinc chloride paste is applied, with the thickness of the layer dependent on the desired depth of penetration; this paste consists of a combination of stibnite, bloodroot powder (Sanguinaria canadensis), and a saturated solution of zinc chloride. (The fixative is used sparingly if tissue conservation is critical, such as when the tumor is located on the nasal ala or pinna of the ear. The penetration of this potent fixative depends on many factors, including the amount applied, the duration of application, the vascularity of tissue, and the type of tissue.)

  • Step 3: The fixative paste is covered with an occlusive dressing to protect the adjacent uninvolved skin, and it remains in place for 6-24 hours.

  • Step 4: After tissue fixation, the fixed-tissue technique is performed in a manner similar to the fresh-tissue technique (ie, with the scalpel angled 45° to the skin, thus beveling the edge, an incision is made in the fixed tissue near the border of the unfixed tissue and continued in the fixed tissue parallel to the skin surface.); following microscopic examination of the tissue sections, additional fixative is applied to any remaining areas of tumor involvement for another 6-24 hours.

  • Step 5: Residual tumor is excised in the same manner as the fresh-tissue technique, generally at a rate of one stage of excision per day.

  • Step 6: When a tumor-free defect is achieved, the remaining fixed tissue is allowed to slough; this process generally takes a few days.

  • Step 7: The defect can then be repaired or allowed to heal by means of secondary intention.

Postoperative Care

Postoperative care following Mohs surgery depends on the type of repair used by the surgeon. Many methods of bandaging and cleansing are acceptable. The principal author's method is described in this section.

Immediate postoperative period

For wounds left to heal by granulation (secondary intention), cleanse the lesion with normal saline solution and then apply topical petrolatum ointment. Instruct patients to do the same 1-2 times a day.

For defects reconstructed with linear closure or flaps, cleanse the surgical site with saline and apply topical petrolatum ointment under a pressure dressing. Instruct patients to leave the bandage alone for 24-48 hours. Subsequently, coach patients to change dressings daily using the same routine (ie, saline and topical petrolatum ointment).

For wounds repaired with skin grafts, place the topical petrolatum ointment directly on the graft, and apply a petrolatum gauze dressing (eg, Xeroform). Place a few layers of sterile 4 × 4–inch gauze atop the petrolatum gauze to provide bulk for a good pressure dressing. Use a liquid dressing adhesive (eg, Mastisol) around the skin a few centimeters from the wound; then, apply paper tape to secure the bulky dressing. Advise patients to leave the dressing untouched until the following week.

Patients are usually given oral antibiotics after undergoing more extensive repairs such as flaps and grafts and for larger wounds.

After wound healing

For patients with extensive photodamage and actinic keratoses near surgical areas, fluorouracil cream, imiquimod cream, or photodynamic therapy can be recommended after the surgical site completely heals. Other superficially ablative techniques (eg, carbon dioxide or erbium: YAG laser) can also be used for skin resurfacing treatments (as cancer prophylaxis).


When any surgical procedure is performed, even under ideal conditions, a risk of complications always exists. In general, complications from Mohs surgery are few and usually minor.[73, 74]

Similar to other dermatologic surgical procedures, the most common postoperative complications from Mohs surgery include bleeding, hematoma formation, nerve damage, seroma formation, wound dehiscence, flap necrosis, graft failure, infection, contact dermatitis due to antibiotic ointments or dressing materials, excessive granulation formation, keloid and/or hypertrophic scar formation, hyperpigmentation and/or hypopigmentation, and tumor recurrence (although the likelihood of tumor recurrence is much less with Mohs surgery than with other more routine therapeutic modalities).

A retrospective study by Cowan et al indicated that compared with the results associated with smaller tumors, Mohs surgery on large tumors is 50 times more likely to produce postoperative complications within 6 weeks of the procedure. The report also found that the risk of postoperative complications was not greater in association with aggressive subclinical extension.[75]


Postoperative bleeding rarely occurs in wounds left to granulate, except when patients neglect the wounds. Postoperative bleeding occurs more frequently with repairs, especially large flaps.

Minimize bleeding risks by obtaining an adequate preoperative patient medical history and having a sound preoperative plan in place (eg, avoidance of nonsteroidal anti-inflammatory drugs [NSAIDs] and acetylsalicylic acid [aspirin] when medically safe; monitor and keep international normalized ratio [INR] < 3 for patients on warfarin).

It is of utmost importance to obtain adequate hemostasis and place a pressure bandage in patients who require continued anticoagulation during Mohs surgery.[76] Studies in recent years have shown that continued usage of warfarin and clopidogrel increases bleeding complications during Mohs surgery—although none of the cases had significant long-term complications. Aspirin, NSAIDs, and vitamin E, however, did not show such increases in postoperative bleeding.

Nerve damage

Sensory nerve loss often occurs during Mohs surgery, because small sensory fibers are severed during tumor excision. Such deficits are usually short term owing to regeneration of the nerve fibers.

Avoid motor nerve damage by applying proper knowledge of human anatomy. Allocate extra time to study the anatomy in high-risk areas where motor nerves travel superficially.


Infections from Mohs surgery are rare with the use of proper cleansing and surgical techniques. For patients with lesions in a surgical site area of high infection risk, oral antibiotics are usually recommended. For wounds involving cartilaginous structures, consider prescribing fluoroquinolones to cover pseudomonal infections.

A study by Nasseri indicated that a single set of sterile surgical instruments can be used for both tumor extirpation and reconstruction in Mohs surgery without subjecting patients to an unacceptable risk of surgical site infection. In the study, just seven surgical site infections occurred among 332 patients (infection rate 2.1%) who underwent Mohs surgery using this technique.[77]



Medication Summary

The goals of pharmacotherapy are to reduce morbidity and prevent complications.


Class Summary

Prophylactic antibiotics are recommended when the surgical site is considered high risk for surgical infection, including the oral mucosa, genitalia, and lower extremities below the knee.


Dicloxacillin is used for the treatment of infections caused by penicillinase-producing staphylococci. It may be used to initiate therapy when staphylococcal infection is suspected.

Cephalexin (Keflex)

Cephalexin is a first-generation cephalosporin that arrests bacterial growth by inhibiting bacterial cell wall synthesis. It has bactericidal activity against rapidly growing organisms. Its primary activity is against skin flora, and it is used for skin infections or prophylaxis in minor procedures.

Clindamycin (Cleocin)

Clindamycin is a lincosamide for the treatment of serious skin and soft-tissue staphylococcal infections. It is also effective against aerobic and anaerobic streptococci (except enterococci). Clindamycin inhibits bacterial growth, possibly by blocking dissociation of peptidyl transfer ribonucleic acid (tRNA) from ribosomes, causing RNA-dependent protein synthesis to arrest.

Doxycycline (Adoxa, Doryx, Vibramycin, Monodox)

Doxycycline is a broad-spectrum, synthetically derived bacteriostatic antibiotic in the tetracycline class. It is almost completely absorbed, concentrates in bile, and is excreted in urine and feces as a biologically active metabolite in high concentrations.

It inhibits protein synthesis and, thus, bacterial growth by binding to 30S and possibly 50S ribosomal subunits of susceptible bacteria. It may block dissociation of peptidyl t-RNA from ribosomes, causing RNA-dependent protein synthesis to arrest. The adult dosage is 100 mg orally twice daily. Severe hepatic dysfunction is a contraindication.

Azithromycin (Zithromax, Zmax)

Azithromycin t is used to treat mild-to-moderate microbial infections. In adults, it is given in a single dose of 1 g orally. Azithromycin acts by binding to 50S ribosomal subunit of susceptible microorganisms and blocks dissociation of peptidyl tRNA from ribosomes, causing RNA-dependent protein synthesis to arrest. Nucleic acid synthesis is not affected. It concentrates in phagocytes and fibroblasts, as demonstrated by in vitro incubation techniques. In vivo studies suggest that concentration in phagocytes may contribute to drug distribution to inflamed tissues.

Trimethoprim and sulfamethoxazole (Bactrim, Bactrim DS, Septra DS)

Trimethoprim/sulfamethoxazole inhibits bacterial growth by inhibiting the synthesis of dihydrofolic acid. The antibacterial activity of trimethoprim/sulfamethoxazole includes common urinary tract pathogens, except Pseudomonas aeruginosa.

Ciprofloxacin (Cipro)

Ciprofloxacin is a fluoroquinolone with activity against most gram-negative organisms but no activity against anaerobes. It inhibits bacterial DNA synthesis and consequently growth.