Collision of Presumed Primary Urinary Bladder Malignant Melanoma and Invasive Urothelial Carcinoma: A Case Report.

"Collision tumors" are a phenomenon that occur when two neoplasms concomitantly localize next to each other. Malignant melanoma of the bladder is an uncommon entity with less than 40 reported instances and is exceedingly rare to present as a collision tumor. In this report, we present a collision tumor consisting of a primary bladder malignant melanoma and invasive high-grade papillary urothelial carcinoma. The clinical presentation and cytomorphologic, immunophenotypic, and molecular findings of this tumor are depicted. Additionally, we also briefly discuss an overview of cutaneous versus mucosal melanomas, focusing on those reported in the genitourinary tract. To the best of our knowledge, this is the second report in literature of a collision between malignant bladder melanoma and urothelial carcinoma occurring in the bladder and the first to involve an invasive urothelial carcinoma.