Collision metastasis: Renal cell carcinoma and prostatic adenocarcinoma to a retroperitoneal lymph node.

Prostatic adenocarcinoma and renal cell carcinoma (RCC) can coexist. However, the incidence of collision metastasis of both prostatic adenocarcinoma and RCC is a rare phenomenon. A 50-year-old non-smoker male with end stage renal disease and a history of prostate adenocarcinoma was noted to have a left renal mass in the upper pole during CT surveillance. With the use of immunohistochemical stains the collision of two distinct malignancies from two different topographical regions was elucidated in a retroperitoneal lymph node. We report the second known case of collision metastasis of RCC and prostatic adenocarcinoma to a retroperitoneal lymph node.