Malignant melanoma metastatic to a basal cell carcinoma simulating the pattern of a basomelanocytic tumor

We report a case of metastatic melanoma colliding with and colonizing a basal cell carcinoma (BCC) on the head of a 69-year-old man. The man had a prior history of multiple primary BCCs and melanomas. One of his primary melanomas, on the left scalp, recurred locally and resulted in the development of numerous in-transit metastases. A bluish nodule was noted on the postauricular area with clinical features consistent with a pigmented BCC. Dermoscopy showed some large gray-blue ovoid structures and blood vessels, features also consistent with BCC. However, the histologic features revealed that the nodule consisted of both metastatic melanoma as well as BCC. Melanoma was present adjacent to as well as within the epithelium of the BCC. The intimate association of melanoma cells within the nodules of BCC simulated the pattern of so-called "malignant basomelanocytic tumor," a recently proposed novel entity. To our knowledge, this is the first description of metastatic melanoma colonizing a BCC.