Collision of Malignant Melanoma and Squamous Cell Carcinoma in Rectum: First Report of a Rare Tumor.

The term collision tumor is used to describe two neoplasms occurring in the same anatomic location with juxtaposition of different tumor elements. Such a coexistence of tumors anywhere in the body is relatively rare. We report a case of 32-year-old female with collision tumor of rectum. The tumor showed two distinct histological patterns with predominant component consisting of malignant melanoma and a minor component of squamous cell carcinoma. The morphological picture of collision was further confirmed by specific immunohistochemical profile of the two tumors. Collision tumors of rectum are uncommon with most of the reported cases comprising adenocarcinoma and neuroendocrine tumors. To the best of our knowledge this is the first case of collision tumor of malignant melanoma and squamous cell carcinoma in the rectum.