Small oncocytic papillary renal cell carcinoma in diabetic glomerulosclerosis

Histologic and immunohistochemical features of oncocytic papillary renal cell carcinoma (RCC) have not been fully elucidated. The author herein report a case of oncocytic papillary RCC (OPRCC). A 71-year-old man with diabetes mellitus and diabetic nephropathy was found to have a small right renal tumor by CT. He had been treated with hemodialysis for chronic renal failure for 10 years. A nephrectomy was performed. Grossly, a small (1.5cm) encapsulated yellow tumor was found in the kidney. Histologically, the tumor was completely encapsulated, and consisted entirely of atypical oncocytes arranged in a diffuse papillary structure with fibrovascular cores. The oncocytes showed grade 3 atypia and pseudostratification. A few mitotic figures were seen, and psammoma bodies, foamy macrophages, and hemosiderin were scattered. Histochemically, the tumor cells were positive for colloidal iron, and negative for mucins (Alcian blue/PAS). Immunohistochemical results of the tumor were as follows: α-methylacyl-coenzyme A rasemase (AMACR) +++, vimentin +++, cytokeratin (CK) 18 +++, CD10 +++, S-100 protein +, MUC1 ++, MUC2 ++, MUC5AC ++, MUC6 ++, panCK Cam5.2 +, CK7 +, CK8 +, CK14 +, CK19 +, CK20 +, p53 +, HepPar1 +, CD68 +, platelet-derived growth factor-α (PDGFRA) +, PanCK AE1/3 -, PanCK WSS -, PanCK MNF115 -, CK 35BE12 -, CK5/6 -, EMA -, desmin -, smooth muscle antigen -, α-fetoprotein -, CEA -, estrogen receptor -, progesterone receptor -, HER2 -, p63 -, and KIT -. Ki67 labeling was 6%. These results suggest that OPRCC can express colloidal iron, low molecular weight CKs, S100 protein, MUC1, MUC2, MUC5AC, MUC6, p53, PDGFRA, and HepPar1.