A rare case of melanoma with Touton-like giant cells: a potential diagnostic pitfall.

: Although approximately 876,000 individuals in the United States currently have a diagnosis of melanoma, the Touton-like giant cell variant has been described only twice in the literature to date. In our case, a 70-year-old man with a history of sclerosing carcinoma on the scalp presented for evaluation of a new nodularity at the site of his previous surgery. On examination, a new complex pigmented lesion on the posterolateral scalp, adjacent to the recurrent sclerosing carcinoma, was noted. Biopsy of the pigmented lesion revealed an invasive melanoma with a Breslow depth of at least 2.78 mm. Microscopic sections showed a predominantly dermal-based tumor composed of sheets and nests of enlarged epithelioid cells. These cells contained oval-to-reniform nuclei with prominent nucleoli and an abundant amount of eosinophilic to vacuolated cytoplasm. Interestingly, numerous multinucleated melanocytes, some with a "Touton" appearance, were scattered throughout the lesion. The lesional cells demonstrated positivity to Mart-1 and HMB-45. Fortunately, the patient's sentinel lymph node biopsy was negative for micrometastases, and a subsequent Position Emission Tomography (PET) scan was unremarkable. Documentation of individual cases of this rare histologic variant of melanoma is necessary given the ability of this lesion to mimic benign histiocytic proliferations at scanning magnification.