Expect Questions About Mohs Micrographic Surgery

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A recent study finding similar overall survival rates for patients with melanomas of the trunk and extremities treated with Mohs micrographic surgery or wide local excision1 raises questions about why and when physicians might recommend, and patients opt for, one or the other procedure.

“The most important factors to consider, at least in my practice, are the size of the tumor, recurrence status, and then clinical margination—how difficult is it to assess the edges of the malignancy from the background skin,” the study’s lead author, Addison Demer, MD, told The ASCO Post. Dr. Demer is Senior Associate Consultant, Department of Dermatology and Assistant Professor at Mayo Clinic, Rochester, Minnesota.

“Tumors on the large size and those that are clinically indistinct or in the background of significant sun damage or on special sites are the ones I would consider for Mohs surgery,” Dr. Demer continued. For melanomas of the trunk and extremities, special sites would be the hands, feet, and nail units. Acral and nail unit melanomas may benefit from Mohs surgery, similar to neck and neck tumors, in that they are special sites where there is not a lot of extra real estate and normal surrounding skin,” Dr. Demer said. He noted, however, that the National Cancer Database used in the study “did not provide a unique distinction for acral and nail unit melanoma.” He also pointed out that the National Comprehensive Cancer Network (NCCN®) “recommends wide local excision universally for all cutaneous melanomas.”

Advantages of Mohs Surgery

“The benefit of Mohs is that it provides complete circumferential peripheral and deep margin assessment,” Dr. Demer noted. With this assessment, “we are able to evaluate the complete periphery and base of the tumor, 100% of the margins. Under the microscope, we can see the entire clinical margin and assess with extreme confidence that the skin cancer is out once the case is complete,” he explained. “We are able to provide complete circumferential peripheral and deep margin assessment in the same-day clinical setting and perform it safely under local anesthesia,” added Dr. Demer.

“We do the tissue processing in real time and prior to repair. The repair can be done in 1 day. You can be confident that you are not doing a complex reconstruction over a site that may still have tumor in it,” Dr. Demer said. “It does take longer on the day of surgery than traditional wide local excision, but the benefit is we are not repairing a wound until we have a 100% certainty that the edges have been checked completely for residual tumor.”

That is not the case for a standard excision, stated Dr. Demer. “A standard excision, when it goes to the pathology lab, is processed like a loaf of bread, and less than 3% of the clinical margin actually gets assessed. The chances of a false-negative margin are fairly substantial,” Dr. Demer noted. “One of the challenges with wide local excision is you may find out from a pathologist a week later that the margin was positive. Sometimes, that’s performed after a large flap or graft repair, which can really be problematic for the patient.”

Recurrence Status

“In general, cure rates with excision for any skin cancer modality after a single or multiple recurrence are lower than those with a primary tumor,” Dr. Demer said. “So, I would consider Mohs surgery for a recurrent tumor, particularly on a special site, or a larger tumor with indistinct margins.”

Dr. Demer addressed the question of which anatomic site benefits from Mohs surgery. “Anatomic sites that are going to require complex repairs, I would argue, benefit from consideration of circumferential peripheral and deep margin assessment. You would hate to do a large flap or graft or a complex repair and have to go back and revise it or completely redo it. That said, if the melanoma is on the back, abdomen, or thigh, and it is an average-sized tumor, the chances of needing to do a complex repair are much lower, as are the chances of needing to take less-than-guideline margins. That is why we don’t see the same recurrence or survival benefit with Mohs surgery on those sites.”  

DISCLOSURE: Dr. Demer reported no conflicts of interest.


1. Demer AM, et al: Association of Mohs micrographic surgery vs wide local excision with overall survival outcomes for patients with melanoma of the trunk and extremities. JAMA Dermatol. October 21, 2020 (early release online).


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