Is the presence of IgG4+ cells within urothelial carcinomas of the renal pelvis that contain rhabdoid and sarcomatoid features associated with IgG4-related diseases?

A 69-year-old male underwent nephrectomy after presenting with a renal mass, as visualized through imaging. Histologic evaluation of the specimen revealed a papillary urothelial carcinoma (UC) in the renal pelvis with infiltration into the renal parenchyma that showed sarcomatoid and rhabdoid features; these features are typically associated with mixed inflammatory infiltrate, storiform fibrosis, and obliterative phlebitis, which is reminiscent of IgG4-related disease (IgG4-RD). Immunohistochemical labeling for IgG4 plasma cells showed that there were >50 cells in a single high-power field and the ratio of IgG4/IgG was >40%; these results are consistent with a diagnosis of IgG4-RD. Herein, we describe the first case of UC that has both sarcomatoid and rhabdoid features and high proportions of IgG4+ plasma cells.