Clear cell papillary renal cell carcinoma with angiomyomatous stroma: a histological, immunohistochemical, and fluorescence in situ hybridization study.

Clear cell papillary renal cell carcinoma (CCPRCC) is a novel tumor entity that was recently recognized as a new distinct epithelial tumor within the current classification system. Nonclassic morphologic variants have rarely been reported. We present six challenging cases of CCPRCC with prominent (>75 %) tubular, acinar, and/or solid component and angioleiomyomatous stroma. The tumors lacked well-organized papillary architecture. All tumors had a variously thick capsule formed by a layer of bands of smooth muscle. The leiomyomatous tissue often entirely encased patches of tubular structures, or it formed only small leiomyomatous islands within the epithelial component. There was a remarkable relationship between the vascular network and the epithelial component in the sense that every single tubule or acinus was associated with a fine capillary network, with the capillaries intimately surrounding the tubular or acinar circumference. CCPRCC with variant morphology expressed carbonic anhydrase IX (CA-IX) in cup-shaped distribution. In addition, the tumor cells stained positive for cytokeratin 34betaE12, CK7, and vimentin. Renal cell carcinoma (RCC), P504s/AMACR, Melan A, and HMB45 were negative in tumor cells in all cases examined. Fluorescence in situ hybridization studies showed the presence of a normal copy number for chromosomes 7, 17, 3q, and 3p. CCPRCC with variant morphology seems to have a favorable prognosis. In the current series, tumor stage was low at presentation, and none of the patients had local recurrence or metastatic disease. The distinction between CCPRCC with variant morphology and clear cell RCC is critical because no case of CCPRCC has behaved aggressively.