Renal Collision Tumor Composed of Clear Cell Carcinoma and Collecting Duct Carcinoma Treated with Nivolumab and Ipilimumab: Case Report and Literature Review

Introduction and importance: Collision tumors refer to the phenomenon where two or more different and unrelated tumors occur in the same location of an organ and form a single lesion. We present the first case of renal collision tumors composed of clear cell carcinoma (ccRCC) and collecting duct carcinoma (CDC) treated with combined therapy of nivolumab and ipilimumab. Case presentation: An 89-year-old male presented to the emergency room with back pain. Imaging studies demonstrated a large tumor in the left kidney with renal vein thrombosis. After radical nephrectomy, the histopathological report showed collision tumors with ccRCC and CDC components. The patient was included in a treatment protocol based on nivolumab (220 mg) and ipilimumab (73 mg) every 21 days, however, obtaining no clinical responses after 5 cycles of treatments. Clinical Discussion: Immune checkpoint inhibitors have become a new standard of care for patients with advanced ccRCC. However, current literatures showed inconclusive evidence on the efficacy of immune checkpoint inhibitor for metastatic CDC. As collision tumors with ccRCC and CDC components were infrequently reported in the literature, we also discuss the histological and immunohistochemical findings, clinical outcomes, and a literature review on this type of renal collision tumors. Conclusion: CDC is a rare and highly aggressive type of renal neoplasms, with limited treatment choices. More studies are needed to evaluate the efficacy of immune checkpoint inhibitors on CDC and its associated collision tumors. Highlights: Collecting duct carcinoma is a rare and highly aggressive type of renal neoplasms, with a poor clinical outcome. Radical nephrectomy alone is rarely curative. The use of immune checkpoint inhibitors for collecting duct carcinoma needs further evaluation. The use of HMWCK as a histologic marker for differential diagnosis of collecting duct carcinoma may need to be evaluated.