Cystic partially regressed clear cell renal cell carcinoma: a potential mimic of multilocular cystic renal cell carcinoma.

AIMS: To study clear cell renal cell carcinomas with predominant cystic and sclerotic components, in which a solid epithelial component precluded a diagnosis of multilocular cystic renal cell carcinoma. We designated these tumours 'cystic partially regressed clear cell renal cell carcinoma.' METHODS AND RESULTS: Twenty-seven tumours were studied, from patients with a median age of 58 years; the stage was most often pT1 (89%). The Fuhrman grade was 2 (48%), 1 (33%), or 3 (19%). The solid epithelial component constituted up to 30% of the tumour volume (median, 10%), whereas the cystic component constituted 15-80% (median, 65%), and the sclerotic component 10-70% (median, 20%). Thin fibrovascular septa lined by cells with clear cytoplasm were almost always present, resembling multilocular cystic renal cell carcinoma. Both zones of sclerosis and fibrovascular septa often contained inconspicuous epithelial cells. Sclerotic areas ranged in appearance from a cellular fibroblastic reaction to scar-like with a residual network of capillaries resembling haemangioma. No patient developed recurrence or metastasis. CONCLUSIONS: Cystic partially regressed clear cell renal cell carcinoma is an uncommon pattern of clear cell renal cell carcinoma, being composed of cysts with solid epithelial and sclerotic components that differentiate it from multilocular cystic renal cell carcinoma.