Desmoplastic melanoma is an often missed lesion and can be the bane of the dermatopathologist's existence. It will resemble a scar, both clinically and histopathologically. When it recurs, it will also resemble a scar and may recur several times before the correct diagnosis is made. Desmoplastic melanoma often presents with a higher Breslow level than other subtypes, but patients do remarkably well given the same pathologic stage and tumor depth, suggesting there is a different biology in these tumors. This case shows a pure desmoplastic histology, and recent studies suggest these rarely metastasize as opposed to their brethren with mixed desmoplastic and conventional histology. Immunohistochemical analysis can be helpful as the tumor will almost uniformly stain with S-100. Other melanocytic markers are typically negative.
At higher power, one can appreciate an atypical spindle cell population within the dermis. The spindle cells show nuclear pleomorphism and moderately abundant pink cytoplasm, intercalating between collagen fibers. Intracytoplasmic pigment is not identified. Focal perineural invasion is present.