Track

Case Reports

Abstract

Dedifferentiated melanoma (DM) is a rare yet aggressive form of melanoma which can be diagnostically challenging due to a loss of conventional melanocytic differentiation and presence of non‑melanocytic phenotypes. In DM, typical melanocytic morphology and immunophenotype are significantly altered which can complicate diagnosis and management. DM can present as a biphasic lesion where one region may retain its conventional melanoma morphology and marker expression, whereas other areas lack these clues pertinent to helping with diagnosis. This poses a major hurdle in identification of DM if specimens are limited only to dedifferentiated tumor. A 39-year-old male with a possible history of melanoma and positive family history presented with two lesions on the right side of his neck that he noticed 6 months prior to biopsy. Both lesions were similar in appearance and presumed to be separate sample sites of the same tumor. They showed ulcerated, poorly-differentiated, epithelioid and pleomorphic tumor cells in sheets. Interestingly, the tumor strongly stained with EMA and diffusely staining with p63 leading to a broad differential including myoepithelial tumors, squamous cell carcinoma, etc. Limited focal staining with Melan-A and SOX-10 supported diagnosis of melanoma but could have been missed if these focal regions were missed during sample procurement or processing, highlighting the complexity of this entity.