Melan‐A positive dermal cells in malignant melanoma in situ

The presence of Melan‐A positive dermal cells in excisions for melanoma in situ represents a frequent conundrum for pathologists. These cells may represent superficially invasive melanoma, benign, incidental, dermal nevi or non‐specific staining of dermal melanophages. Occasionally, rare, Melan‐A positive dermal cells are present which do not clearly correspond to the above three categories. Our objective was to further characterize these Melan‐A positive dermal cells. To do this, immunoperoxidase staining for Melan‐A and SOX‐10 was performed on 188‐cutaneous excisions, including examples of melanoma in situ, atypical junctional melanocytic hyperplasia and non‐melanocytic tumors. These were evaluated for the presence of Melan‐A and SOX‐10 positive dermal cells. Dermal cells, positive for both markers, were identified in 17% of the excisions. The cells were present in 10% of cases from the melanocytic group and 31% of the cases from the non‐melanocytic group. These cells did not exhibit cytologic atypia and resembled neither the co‐existing neoplasm nor melanophages. We conclude that positivity of these rare Melan‐A positive cells for SOX‐10 argues that they represent true melanocytes and not non‐specific staining. The absence of cytologic atypia in these cells and their presence in excisions of non‐melanocytic neoplasms argues that they are benign, reactive, dermal melanocytes.