Making the distinction between LM and AJMH common to chronically sun-damaged skin is no easy task. Dr. Bowen cited a concordance study between dermatopathologists interpreting staged excisional margins on permanent sections for LM where the concordance was only moderate at best. In this study, the use of a negative control improved the concordance rate on “difficult” cases from 46% to 76%; P = .001 (Arch Dermatol. 2003 May;139(5):595-604). “What we really need is a molecular marker that will tell us if a melanocyte is malignant or not,” he said. “All we have now are immunostains that tell you if it’s melanocyte but nothing more.” He went on to say that in multivariate analysis in two studies of the histologic features of LM, the only feature that consistently predicted the difference between LM and AJMH was the melanocyte density and its ratio to the negative control (Dermatol Surg. 2011;37(5):657-63 and J. Plast. Reconstr. Aesthet. Surg. 2014;67(10):1322-32). “The MART-1 immunostain is extremely sensitive, but it makes the slide somewhat muddy, so it’s hard to do an accurate cell count,” he said. “For that reason, we also use a SOX-10 immunostain which is very specific but not as sensitive. I believe that the truth lies somewhere in between those two immunostains in light of a positive control from our lab and a negative control from the patient.”
He concluded that the neoadjuvant use of imiquimod followed by a conservative staged excision “allows me to clear 90% of LM with a 2 mm margin with a recurrence rate of 2.3% in patients with a mean follow-up of 5-years or greater.”
Dr. Bowen reported having no financial disclosures.