Clear cell papillary renal cell carcinoma with characteristic morphology and immunohistochemical staining pattern

Clear cell papillary renal cell carcinoma is newly-defined entity initially believed to be associated with end stage renal disease. We report a rare case of this neoplasm in a 70-year-old female patient with no known history of end-stage renal disease who presented with haematuria lasting several days. After initial workup, a computed tomography (CT) scan was performed and revealed a cystic mass in the right kidney. Material obtained by fine needle aspiration (FNA) biopsy of the mass was felt to be suspicious for renal cell carcinoma. The patient subsequently underwent right nephrectomy, and the lesional tissue was examined microscopically. A 2.3 cm in greatest dimension cystic space circumscribed by a fibrous wall was surfaced by a single layer of bland cuboidal cells with abundant clear cytoplasm. The solid component of the tumour consisted of branching papillae with delicate fibrovascular cores and uniformly lined by cells similar to those of the inner wall of the cyst. Some of the fibrovascular cores were markedly expanded by a myxoid-appearing substance, but no foamy cells were appreciated. Immunohistochemically, the neoplastic cells were diffusely immunoreactive with cytokeratin 7 (CK7), epithelial membrane antigen (EMA), high molecular weight cytokeratin (HMWCK) and vimentin. Neoplastic cells were only focally immunoreactive with CD10, and were negative for both p63 and alpha-methylacyl-CoA racemase (AMACR) (P504S). The cytomorphological features and immunohistochemical staining pattern of this tumour was consistent with that of clear cell papillary renal cell carcinoma (CCPRCC), as described by Gobbo et al.