Mohs Surgery Workup

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