Periungual Amelanocytic Malignant Melanoma with Osteocartilaginous Differentiation of the Right Hallux: A Case Report.

Malignant melanoma with osteocartilaginous differentiation is extremely rare. We report a case of periungual osteocartilaginous melanoma (OCM) on the right hallux. A 59-year-old man presented with a rapidly growing mass with drainage on his right great toe after treatment of ingrown toenail and infection 3 months earlier. Physical examination showed a 2.0×1.5×1.0-cm, malodorous, erythematous, dusky, granuloma-like mass along the fibular border of the right hallux. Pathologic evaluation of the excisional biopsy revealed diffuse epithelioid and chondroblastoma-like melanocytes with atypia and pleomorphism in the dermis with strong SOX10 immunostaining. The lesion was diagnosed as osteocartilaginous melanoma. The patient was referred to a surgical oncologist for further treatment. Osteocartilaginous melanoma is a rare variant of malignant melanoma that needs to be differentiated from chondroblastoma and other lesions. Immunostains for SOX10, H3K36M, and SATB2 are helpful for the differential diagnosis.