A series of collision tumors in the genitourinary tract with a review of the literature.

Collision tumors, characterized by the coexistence of phenotypically and genotypically distinct tumors at the same site, are distinctly rare in the genitourinary tract and pose a diagnostic challenge. The goal of this study is to present a series of such cases from a single institution highlighting the unusual clinicopathologic features of these tumors. Six cases were retrospectively identified from our surgical pathology files and included internal and consultation cases (2006-2012). All tumors were identified by H&E and selected immunohistochemistry. There were 5 males and 1 female patients ranging in age from 57 to 84 years (average 73 years). The sites of these collision tumors were located in the kidney (3 cases), bladder (2 cases), and prostate. All collision tumors involved at least one malignant neoplasm. The diagnosis of collision tumors in the genitourinary tract is a perplexing task. Awareness of these rare entities, thorough sampling of the tumor mass, and appropriate use of ancillary techniques to demonstrate the different tumor components can help avoid an incorrect diagnosis, as well as with pathologic staging.