Results significant, but not surprising
of members of the American College of Mohs Surgery.
Of 513 survey participants, 40.9% reported using MMS to treat any subtype of melanoma. Most of these surgeons reported treating both lentigo maligna (97.5%) and other melanoma in situ (MIS) subtypes (91.4%). A slight majority – 58.6% – reported treating invasive T1 melanoma, and 20.5% reported treating invasive T2 and/or higher-stage melanoma with MMS.
The analysis, published in Dermatologic Surgery, was done by Spyros M. Siscos, MD, and a team of residents and faculty in the division of dermatology at the University of Kansas Medical Center, Kansas City.
It comes on the heels of an analysis of claims data for Mohs surgery, published last year in JAMA Dermatology, which showed a more than threefold increase in the use of Mohs surgery for melanoma from 2.6% of all surgical cases in 2001 to 7.9% in 2016.
With the increased use of MMS for treatment of melanoma, “Mohs surgeons who previously treated MIS with MMS may be increasingly doing so and/or expanding their scope of treatment to include invasive melanoma,” the University of Kansas investigators wrote.
That a slight majority now report treating invasive melanoma with MMS “may be due, in part, to upstaging during the MMS procedure and the increasing evidence demonstrating improved survival of early-invasive melanoma treated with MMS compared with [wide local excision],” as well as the advent of melanocytic immunohistochemical (IHC) stains, particularly melanoma antigen recognized by T-cells 1 (MART-1), they said. However, 29% of surveyed Mohs surgeons treating melanoma with MMS do not use IHC stains “despite growing evidence supporting” their use, the authors wrote.
The advent of IHC stains, particularly MART-1, has improved the accuracy of interpreting frozen sections of melanoma, they reported, noting that MMS without IHC has been associated with a recurrence rate as high as 33%. Of the 71% who reported using IHC stains, MART-1 was the primary IHC stain for virtually all of them (97.3%).
There was also variation in the number of surgeons who reported debulking MIS. Eighty-two percent take this approach, excising the clinically visible tumor before excising the initial Mohs stage – almost all with a scalpel. More than half of these surgeons – 58.5% – submit the entire debulked MIS specimen for permanent vertical sectioning (breadloafing) to evaluate for deeper tumor invasion.
The others reported submitting the entire debulked specimen for frozen vertical sectioning, or portions of the specimen for both permanent and frozen vertical sectioning. “It is unclear why a minority of surveyed Mohs surgeons reported not debulking MIS,” wrote Dr. Siscos and his colleagues.
The average margin size of the first Mohs stage for MIS was 4.96 ± 1.74 mm, which is at the lower end of the 0.5-1.0 cm range for wide local excision (WLE) recommended by the National Comprehensive Cancer Network (NCCN) and the American Academy of Dermatology (AAD), according to a clinical practice guideline. (The survey did not investigate initial margins for invasive melanoma treated with MMS.)
Jeremy R. Etzhorn, MD, of the department of dermatology at the University of Pennsylvania, Philadelphia, and an author of a 2019 claims data analysis of excisional surgery practices for melanoma, said that the new survey findings – like the prior analysis – highlight the variability in approaches to using MMS for melanoma.
“Mohs for melanoma [seems] like a one-liner ... but really, there are [a lot] of different techniques that fall under that umbrella, if you parse out all the variations,” he said in an interview.
Per the 2016 claims analysis, he noted, IHC was used in less than 40% of Mohs surgery cases for melanoma, and there were wide geographic variations. “The biggest critique of Mohs surgery for melanoma over the last two decades has been that it’s hard to see the tumor,” he said. “But with the advent of IHC, that challenge was overcome.”
Surgical excision practices are evolving without the development of best practice guidelines, said Dr. Etzkorn, who is director of clinical research for the University of Pennsylvania dermatologic oncology center. Multisociety guidelines published in 2012 on appropriate use criteria for Mohs surgery do not offer specific recommendations on the use of MMS for invasive melanoma. Nor do guidelines from the AAD and the NCCN, he said.
“What this [new] study highlights and what’s being discussed amongst Moh’s surgeons” is that Mohs for melanoma “has be to be standardized” to some extent and then clinical trials conducted comparing Mohs to conventional excision. The studies that have been published in recent years comparing MMS with WLE for MIS and invasive melanoma are “not gold standard studies,” he said.
Practice guidelines then can be informed by high-quality evidence on its safety and efficacy, he said.
The 513 participants in the newly published survey represent a 31.5% response rate. Invasive T2 and/or higher stage melanoma was more likely to be treated with MMS in academic hospitals, compared with other practice settings (30.2% v. 18.1%), Dr. Siscos and his coauthors reported.
Participants who reported treating melanoma with MMS were more likely to report fellowship exposure and more likely to have received fellowship training on melanocytic IHC stains. The study “highlights the importance of fellowship exposure to MMS and IHC staining for melanoma,” the authors wrote, adding that postfellowship training opportunities in MMS and IHC staining for melanoma may help broaden its use among Mohs surgeons who received inadequate fellowship exposure.
Dr. Siscos and his colleagues reported no significant interest with commercial supporters. Dr. Etzkorn had no disclosures.
SOURCE: Siscos S et al. Dermatol Surg. 2020 Oct;46(10):1267-71.