Cystic renal cell carcinoma: biology and clinical behavior.

The purpose of the study was to evaluate unilocular and multilocular cystic renal cell carcinoma (cRCC). These tumors are a rare entity, comprising approximately 1 to 2% of all renal tumors, and their true biologic behavior is not well-known. Initial review of renal cell carcinoma (RCC) cases treated at our institution between 1989 and 2001 identified 39 cases of cRCC. However, histopathologic review of these cases by 2 pathologists revealed that only 18 cases met the criteria that all tumors have a cystic component that constitutes at least 75% of the total lesion without evidence of necrosis. These cases were compared to 614 conventional clear cell RCC cases with regards to clinical outcomes. All 18 patients presented with localized (N0M0) disease. Thirteen (72%) of the tumors were Fuhrman Grade 1, while the remaining 5 (28%) were Fuhrman Grade 2. By comparison, only 60% of the clear cell RCC tumors were Grade 1 or 2. Similarly, 83% of cRCC were pT1 tumors compared to only 35% of conventional clear cell tumors. Mean tumor size for the cRCC tumors was 4.9 cm compared to 7.4 cm for conventional clear cell tumors. Cystic RCC patients had an 82% four-year disease-specific survival (DSS). Unilocular and multilocular cRCC is a distinct subtype of clear cell RCC. Its biology appears to be more favorable with regards to important prognostic factors such as metastatic presentation, Fuhrman grade, 1997 T stage, and tumor size. These findings suggest that cRCC patients may benefit from nephron sparing surgery.