Collision tumor of malignant skin cancers: A case of melanoma in basal cell carcinoma

The coexistence of two malignant skin tumors intermingling in the same histologic specimen is rare. We report a case of melanoma in a basal cell carcinoma collision tumor. The presence of two intermingled neoplasms was confirmed by immunohistochemistry, which showed strong positivity for S-100 and HMB-45. A review of the literature and a case analysis allow for some pathogenetic and prognostic considerations.