Shane A. Meehan, MD
Molecular assays are a driving force in diagnosing a broad array of tumor types, and while molecular diagnostics assays are propelling the field of oncology forward, Shane A. Meehan, MD, emphasizes the important role that immunohistochemistry (IHC) still has—especially for diagnosing melanoma.
“Molecular diagnostics is a new front. It has been around for 5 years,” said Meehan during the 2017 OncLive®
State of the Science SummitTM
on Melanoma and Immuno-Oncology. “IHC has been around for decades. There is almost a tendency to say, ‘Hey, we got these newer molecular diagnostic tests. This is where we need to go.’ In fact, there is still a lot that IHC can help us with.”
Shane A. Meehan, MD, associate professor, Ronald O. Perelman Department of Dermatology, associate professor, Department of Pathology, director of the Dermatopathology Fellowship Training Program, and director of the Dermatopathology Section at New York University Langone Medical Center in New York, discussed the continued importance of IHC testing, even with the emergence of novel molecular assays, in an interview during the meeting.
OncLive: Could you discuss the highlights of your lecture?
I want oncologists to know about how important IHC is in the analysis of melanocytic lesions. It is important, but there are a limited number of applications and, primarily, the most important application is the use of IHC to determine melanocytic differentiation when one sees a poorly differentiated tumor.
We have, in our armamentarium, a variety of antibodies to use in order to determine that melanocytic differentiation. Those are S100, SOX10, MelanA, HMB45, and there are others. The most sensitive and specific markers are S100 and SOX10 in addition to MelanA. Then, depending on the particular profile of these markers and what particular antigens they can stain, 1 might be more useful for the diagnosis of desmoplastic melanoma than the diagnosis of melanoma in situ.
As dermatopathologists, we weigh the pros and cons of each of these antibodies in how to work up a melanocytic lesion depending on our suspicion of its particular type. There are other markers that we can use besides the melanocytic ones, a lymphatic one called D240, and also a proliferation marker called Ki-67. We have to be wary of the potential pitfalls of any 1 of these markers. We use them all in our assessment in melanocytic lesions as we arrive at the diagnosis of melanoma.
You can detect these markers with the use of IHC?
Most of these markers that I talked about are only useful in determining the nature of a tumor as being melanocytic. Ki-67 is a proliferation marker. Once we determine that a marker is of a melanocytic lineage—that it’s either melanoma or nevus—we can use other markers, such as Ki-67, a proliferation marker. That would show it’s more likely something atypical, like a melanoma rather than a nevus. A proliferation marker, in that instance, may not show much staining, but if it does show a lot of staining, then we have to be concerned about a melanoma diagnosis.
Are there any ongoing research studies looking more in depth at these markers?
Every few months, another marker comes on the market as the “new kid on the block,” whether or not [it’s really] more sensitive or specific. Over time, we know whether or not a particular marker is tried and true.
An example of a more recent marker is p16, a cyclin kinase inhibitor. Initially, it showed much promise and tends to have decreased expression in melanomas. With experience, it turned out there are issues with regards to specificity with p16, so it is maybe not the “magic bullet” that people thought it would be.