Mohs for Melanoma Immunohistochemistry

In this interview, Dr Addison Demer discusses the session he moderated, “Mohs for Melanoma Immunohistochemistry Refresher,” at the 2023 ACMS Annual Meeting.

Addison M. Demer, MD, is an assistant professor and Mohs micrographic surgeon at the Mayo Clinic in Rochester, MN.

The Dermatologist: Can you give us a recap of what was covered during the session at the 2023 ACMS Annual Meeting?

Dr Demer: The American College of Mohs Surgery (ACMS) put on a full bootcamp webinar on MART-1 staining that was conducted in the fall of 2022. Our session was essentially a more brief version of the full bootcamp. We had 3 presenters other than myself. Dr Tyler Hollmig was my comoderator and he is an associate professor at The University of Texas at Austin. He talked about indications in techniques for Mohs for melanoma, followed by Dr Justin Leitenberger, who is an associate professor at Oregon Health and Science University. He talked about interpretation of MART-1 immunohistochemistry (IHC) when performing IHC-driven Mohs for melanoma cases. And then we finished the session with a great presentation by Dr Sama Carley, who is in private practice in San Diego, and she talked about the practical establishment of melanoma IHC in your Mohs practice.

The Dermatologist: Can you elaborate on the IHC-guided Mohs surgery for melanoma?

Dr Demer: Mohs for melanoma has been kind of controversial and a contentious topic. In large part this is because the traditional dogma is such that melanomas should be evaluated with permanent section hematoxylin-eosin stains. There are some limitations with the frozen section processing and freeze artifact that can make it more challenging to appropriately delineate melanocytes when looking at frozen section slides. The best way to mitigate the artifactual challenge is to perform IHC stains specific to melanocytes, which allow us to, on frozen sections, see each individual melanocyte such that we can accurately in real time interpret our marginal sections. This has been a great tool for us to be able to get same-day marginal interpretation with Mohs while working around the traditional limitations of frozen sections.

The Dermatologist: Can you go over the key points from the session in detail?

Dr Demer: The first speaker, Dr Hollmig, talked about indications and techniques for Mohs for melanoma. He essentially provided evidence in the literature for Mohs for melanoma and highlighted some of the important considerations in terms of tumor and patient selection, location, and the evidence behind most melanoma. Importantly, he shared the growing body of evidence suggesting that melanomas treated with Mohs with IHC are associated with the lowest recurrence rate when compared to wide local excision for head and neck tumors. And he briefly touched on some evidence suggesting that tumors of the head and neck treated with IHC-guided Mohs surgery may be associated with an improved survival when compared to traditional excision. He went on to share an excellent approach to performing Mohs surgery while highlighting a great article published by the Penn group, which goes through, step by step, an ideal way to process the tissue. In particular, this starts with taking a deep bulk of the tissue for vertical sectioning, such that we can get appropriate staging information, followed by taking a layer around and under the previous deep bulk, such that you can get complete peripheral and deep margin assessment in real time.

The next topic was covered by Dr Leitenberger, and that was IHC interpretation of MART-1 stain. He talked about the criteria for diagnosing melanoma and invasive melanoma on IHC slides. He essentially went over the main criteria for recognizing melanoma on MART-1, which includes contiguous junctional melanocytes 10 and more, lining up along the basal layer, upward migration of pagetoid spread of melanocytes, follicular extension beyond the follicular infundibulum, and nuclear atypia, as well as atypical nests of 3 or more cells, some of which are not in contact with the basement membrane. He went over these criteria that we can use to make the call as to whether an area of margin is in fact positive. He then went over common pitfalls and mimickers, including nonspecific dendritic or dermal staining, what to do when we encounter benign intradermal nevi, and how to contrast nevi from invasive melanoma. And he reviewed some important factors in terms of how to optimize site preparation while recognizing potential artifacts.

The third section of our talk was the topic of establishing melanoma IHC in your clinical practice. Dr Carley has a private practice, which has recently embarked on the process of performing IHC. She went over the important steps in terms of regulation and documentation, Clinical Laboratory Improvement Amendments and College of American Pathologists certification, and all the paperwork and logistics that you must have in place to appropriately perform and document IHC in your Mohs practice. She also talked about the various ways that you can perform IHC in your practice, including hand-dipped staining protocols and contrast to machine-staining protocols. She also compared and contrasted rapid immunostains to the traditional longer immunostain protocols. She showed great photos and video on how to perform this in your clinics. In particular, she showed a hand-dipped staining protocol that they use in their practice.

The Dermatologist: What additional tips and insights would you like to share with your colleagues regarding Mohs for melanoma IHC?

Dr Demer: We know based on data from a recent survey at the ACMS that the majority of ACMS members feel IHC frozen sections can be performed for Mohs for melanoma safely and reliably. However, a minority of ACMS members actually perform frozen section IHC in their practice. Only 40% of respondents in our survey use at least one IHC stain during Mohs surgery. The vast majority of those who do perform IHC are using MART-1 for melanomas. We asked the folks who are not performing this in their practice, why not? We found that they cite startup costs and a lack of formal education. Fifty-one percent said they do not feel formally trained and have a lack of confidence in reading immunostaining in addition to it being time consuming.

What I would like to offer is reassurance that this is a process and a skill that can be learned, and we are fortunate that the ACMS is developing curricula and has put on things like the MART-1 bootcamp such that dermatologists and most surgeons are able to become comfortable reading IHC melanoma cases. And hopefully by having a universal standard of formal education, and sharing information that this can be done cost effectively and in a way that is not overly time burdensome with rapid immunostaining protocols, we will be able to make some headway in closing the gap between the 40% of folks who are currently performing this and the 92% of folks who feel this is a reliable way of approaching special assignments.

Reference:
Demer AM. Mohs for melanoma immunohistochemistry refresher. Presented at: American College of Mohs Surgery (ACMS) Annual Meeting; May 4–7, 2023; Seattle, WA.

Watch Dr Demer's interview video!