Cystic renal cell carcinoma carries an excellent prognosis regardless of tumor size.

INTRODUCTION: Cystic renal cell carcinoma (cystic RCC) is thought to carry an improved prognosis relative to clear cell RCC (CCRCC); however, this is based on small case series. We used a population-based tumor registry to compare clinicopathologic features and cancer-specific mortality (CSM) of cystic RCC with those of CCRCC.

MATERIALS AND METHODS: The Surveillance, Epidemiology, and End Results database was queried for all patients diagnosed and treated for cystic RCC and CCRCC between 2001 and 2010. Clinical and pathologic factors were compared using t tests and chi-square tests as appropriate. Kaplan-Meier survival analysis compared CSM differences between cystic RCC and CCRCC.

RESULTS: A total of 678 patients with cystic RCC and 46,677 with CCRCC were identified. The mean follow-up duration was 52 and 40 months, respectively. When compared with CCRCC patients, those with cystic RCC were younger (mean age 58 vs. 61 y, P < 0.001), more commonly black (22% vs. 9%, P < 0.001), and female (45% vs. 41%, P = 0.02). Cystic RCCs were more commonly T1a tumors (66% vs. 55%, P < 0.001), well differentiated (33% vs. 16%, P < 0.001), and smaller (mean size = 3.8 vs. 4.5 cm, P < 0.001). Cystic RCC was associated with a reduction in CSM when compared with CCRCC (P = 0.002). In a subset analysis, this reduction in CSM was seen only for those with T1b/T2 tumors (P = 0.01) but not for those with T1a RCCs lesions (P = 0.31).

CONCLUSIONS: We report the largest series of cystic RCC and corroborate the findings of improved CSM when compared with CCRCC for larger tumors; however, no difference was noted in smaller tumors, suggesting that tumor biology becomes more relevant to prognosis with increasing size. These data may suggest a role for active surveillance in appropriately selected patients with small, cystic renal masses.