Synchronous Primary Renal Lymphoma and Renal Cell Carcinoma: Collision Tumors in the Same Kidney.

Background: Primary renal lymphoma (PRL) is an exceptionally rare disease with under 50 reported cases in the literature. PRL is an aggressive condition that can present with nonspecific symptoms and local invasion mimicking renal cell carcinoma (RCC). We present an unusual case involving a collision tumor between PRL and RCC. Case Presentation: The patient is a 62-year-old immunosuppressed man with an incidental left renal mass on cross-sectional imaging. Renal mass biopsy confirmed clear cell type RCC. He underwent robot-assisted, laparoscopic left radical nephrectomy for presumed RCC without evidence for extrarenal disease or discernable lymphadenopathy. Final pathology revealed a collision tumor, including PRL and RCC. Conclusion: To our knowledge, this is the first reported case within the literature describing a collision tumor between PRL and RCC. Although rare, it is important to consider PRL in the differential diagnosis of a solid renal mass, especially in patients with a prior history of transplantation and/or chronic immunosuppression.