Natural History of Complex Renal Cysts: Clinical Evidence Supporting Active Surveillance

Purpose: We evaluated intervention rates, progression and cancer specific survival outcomes in patients with complex renal cysts in a single center experience. Materials and Methods: We used the Montage (TM) radiology data mining system to retrospectively identify all reported cases of complex renal cyst at our institution from 2001 to 2013. The primary study end points were overall and cancer specific survival. The secondary end points included radiographic progression and upgrading, clinical progression and final histology on surgical pathology. Results: We identified 336 patients with a complex renal cyst, of whom 185 (55.1%), 122 (36.3%) and 29 (8.6%) had Bosniak IIF, III and IV cysts, respectively. Median followup was 67.1 months (range 34.4 to 101.6). In the 332 patients with followup there was 1 cancer specific death (0.3%) and overall mortality was 6.2%. Ten (5.4%), 37 (30.3%) and 18 patients (62.1%) with Bosniak IIF, III and IV, respectively, underwent surgical or ablative intervention. The indication for intervention was predominantly age (intervention vs no intervention mean +/- SD age 50.1 +/- 15.9 vs 62.5 +/- 13.9 years) and complexity. Surgery with radical and partial nephrectomy (23 patients or 35% and 37 or 57%, respectively) was most common and favorable final pathology was identified. Two treated patients experienced recurrence during followup. When excluding patients with von Hippel-Lindau syndrome, the cancer specific survival rate was 100%. Conclusions: Cancer survival and overall survival in patients with Bosniak IIF to IV renal cysts was high with only 1 cancer specific death. No cancer deaths were recorded in patients who did not undergo intervention. Reconsidering management guidelines for complex renal cysts is warranted, particularly consideration for initial surveillance of Bosniak III cysts.