Clear cell papillary renal cell carcinoma: a distinct low-grade renal tumour

Abstract

To study the clinicopathologic features of clear cell papillary renal cell carcinoma (CCPRCC). The clinical, morphologic and immunohistochemical characteristics of 6 cases of CCPRCC were reviewed, with analysis of follow-up data. There were altogether 3 men and 3 women. The mean age of patients was 56 years. The size of tumors ranged from 1.0 to 4.5 cm in greatest dimension. They had solid or solid-cystic cut surface. Histologically, the tumors were encapsulated and showed several morphologic patterns, with tubules, papillae, acini, interconnecting ribbons and macro/microcysts lined by single layer of cells with clear or small amount of eosinophilic cytoplasm and low-grade nuclei (corresponding to Fuhrman grade 1 or 2). Mitotic figures were rarely seen. Characteristically, there was linear arrangement of the nuclei away from the basement membrane, conferring an appearance similar to that of endometrial glands in early secretory phase. Tubules and cysts contained serosanguineous fluid or colloid-like secretion were identified. No foamy histiocytes, psammomatous calcifications or hemosiderin was present in the papillary areas. Two of the tumors showed focal or extensive angioleiomyoma/leiomyoma-like components. No coagulative necrosis, sarcomatoid dedifferentiation, nor microscopic vascular invasion was observed. Immunohistochemically, all tumors showed strong co-expression of CK7 and CA9 (with characteristic "goblet" staining pattern). The staining for EMA, CK (AE1/AE3), vimentin, CK8, CK18, CK19 and PAX-8 were also positive in all cases. Ki-67 was expressed in less than or about 5% of the tumor cell nuclei. The staining for CD10, P504S, CD117, TFE3 and TFEB was negative. Follow-up data were available in all patients, with mean duration of 14 months (range = 7 to 27 months). All of the patients were disease-free after operation. CCPRCC is a special type of low-grade renal neoplasm with characteristic histopathologic and immunohistochemical features. It needs to be distinguished from clear cell renal cell carcinoma or papillary renal cell carcinoma.