Track

Basic Science

Abstract

Distinguishing melanoma cells from nevus cells remains a diagnostic challenge, particularly in cases where melanoma exhibits nevoid morphology or nevus cells display atypical or epithelioid features. Accurate identification is essential for proper measurement of Breslow depth in melanomas arising within nevi and for margin assessment—both of which are critical for patient prognosis. The dual multiplex immunohistochemical stain utilizing Melan-A (red chromogen) and Ki67 (brown chromogen) is a valuable tool for assessing the proliferative index of melanocytic populations, with melanoma cells typically showing a higher Ki67 index than nevus cells. In addition to this proliferative difference, we have observed that melanoma cells demonstrate more intense Melan-A red chromogen labeling than the adjacent nevus cells. This differential labeling provides a helpful visual distinction between melanoma and nevus cells within the same histologic section, further enhancing diagnostic confidence. In this case series, we illustrate this phenomenon with representative examples, quantify the differences in Melan-A staining intensity, and explore potential biological mechanisms that may underlie this observation.