Synchronous Diffuse Large BCell Lymphoma Identified During Retroperitoneal Lymph Node Dissection for Stage III Clear Cell Renal Cell Carcinoma: A Case Report.

Background & Objective: NonHodgkin lymphoma (NHL) and renal cell carcinoma (RCC) are common malignancies, and survivors of either are at increased risk of second primary cancers. Synchronous presentation of diffuse large Bcell lymphoma (DLBCL) with clear cell RCC (ccRCC) is rare. Case Report: An 82yearold man presented with right flank pain and gross hematuria. Imaging showed an 11.3 × 8.0 cm enhancing right renal mass with extension into the renal vein and inferior vena cava and multiple paraaortic lymphadenopathies. He underwent radical right nephrectomy with perirenal and retroperitoneal lymphnode dissection. Kidney histology showed ccRCC, ISUP grade 4, with extension to the renal sinus and renal pelvis. Retroperitoneal nodes were infiltrated by large atypical Bcells positive for CD20 and PAX5 and negative for CD3, CD15, and CD30, with Ki67 ~50%, consistent with DLBCL. A postoperative wholebody PET/CT showed no residual malignancy. Treatment and outcome: He received six cycles of RCHOP for DLBCL and adjuvant pembrolizumab for highrisk ccRCC. He remains in complete remission four years after diagnosis. Conclusion: This case illustrates the possibility of synchronous primary DLBCL in patients undergoing surgery for RCC. Routine pathological evaluation of dissected nodes can change staging and management.