Melanoma histologically mimicking granulomatous inflammation

Summary: A 69-year-old male without prior history of skin disease presented with a 1 cm asymmetrical pink plaque with central gray-brown pigmentation on the left lower cheek that had become more raised and pruritic over several months. The rest of the physical exam was unremarkable. Clinical examination was concerning for melanoma, and a shave biopsy was performed. On low power, histologic exam demonstrated pseudoepitheliomatous hyperplasia with nodular dermal aggregates. Prominent multinucleated giant cell formation was observed which mimicked granulomatous inflammation. Higher power showed intraepidermal and nodular aggregates of atypical melanocytes, extending into the reticular dermis where the sample was broadly transected. There was no evidence of infection or foreign material; PAS, Gram, GMS, and AFB stains were negative for microorganisms. Fontana Masson stain highlighted melanin deposition while Prussian blue iron stain was negative. Immunohistochemical staining for melanoma markers (SOX-10, PRAME) confirmed that the multinucleated giant cells were melanocytes. Melanoma can present with features mimicking benign and malignant non-melanocytic proliferations. Although melanocytic giant cells and granulomatous inflammation in melanoma have been previously described in the literature, to our knowledge, melanoma mimicking granulomatous inflammation on histology has not been previously reported. The patient was subsequently referred to a multidisciplinary pigmented lesion clinic for further management.