Synchronous clear cell renal cell carcinoma and clonal plasmacytoid cell infiltration: A case report and literature review.

Recent studies of tumor microenvironments have revealed that clonal B cells reacting to tumor-derived antigens play an important role in anti-tumor immunity. We report a case of a 72-year-old Japanese man with a complaint of fever for 1 month. Computed tomography revealed a 48 mm mass in his right kidney. The patient underwent a right nephrectomy and histology revealed clear cell renal cell carcinoma (ccRCC) of Fuhrman Grade 4 with rhabdoid morphology. Focally, marked plasmacytoid cell infiltration was detected in the carcinoma. These plasmacytoid cells were immunohistochemically positive for immunoglobulin (Ig) G, and kappa light chain restriction was confirmed using mRNA in situ hybridization. Programmed death-ligand 1 (PD-L1) immunostaining and RNA in situ hybridization of transforming growth factor beta (TGF-β) revealed that both PD-L1 and TGF-β were highly expressed in the area with clonal plasmacytoid cell infiltration. The patient developed bone metastasis 3 months after surgery, and plasmacytoma was not detected during the observation period. We identified a potential link between an immunosuppressive microenvironment and clonal B cell proliferation. The latter posed a differential diagnosis problem between reactive and neoplastic clonal B cell proliferation vis-à-vis a plasmacytoma complicating carcinoma.