Retroperitoneal lipoma and bilateral renal cell carcinoma in a rare co-existence

Introduction: Giant retroperitoneal lipomas are rarely observed clinically, and a retroperitoneal lipoma accom-panied by renal cell carcinoma is even more unusual. We present a case of a large retroperitoneal lipoma with bilateral renal cell carcinoma that was definitively diagnosed after resection.Case presentation: A huge retroperitoneal mass was incidentally discovered in a 58-year-old male with end stage renal disease being evaluated for a kidney transplant. Imaging studies revealed a mixed solid and fat-containing mass displacing the left kidney. Repeat imaging discovered concurrent unilateral renal cell carcinoma and in-terval enlargement of the mass. Histopathology showed benign adipose tissue, bland spindle cells, and mixed inflammatory infiltrate that was negative for MDM2 amplification. Resection of the mass and bilateral ne-phrectomy was performed. Final histopathological examination was consistent with bilateral renal cell carci-noma and a large benign retroperitoneal lipoma. Discussion: The presented case provides a prime example of the diagnostic challenges encountered with retro -peritoneal tumors, The final diagnosis of lipoma in this case was only made after review of the resected specimen in its entirety. Retroperitoneal lipomas can present differently based on tumor size and involvement of adjacent organs. The concomitant occurrence of a renal cell carcinoma and retroperitoneal lipoma is extremely rare, and this is the first report published in the literature.Conclusion: We document a rare case of retroperitoneal lipoma with concurrent bilateral renal cell carcinoma and illustrate frequently encountered challenges during the evaluation of retroperitoneal masses.