Mohs Surgery

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