Long-term oncological outcomes of cystic renal cell carcinoma according to the Bosniak classification

Objectives: To evaluate the prognostic role of the Bosniak classification on the long-term oncological outcomes of cystic renal cell carcinomas. Material and method: In a national multicentric retrospective study, we included patients treated surgically for localized cystic RCC from 2000 to 2010. Patients with a follow-up of less than 4 years, benign tumors, and ablative treatments were excluded. The primary outcome was disease-free survival. Results: 152 patients met the inclusion criteria: Bosniak II (6%), III (53%), IV (41%), with a median follow-up of 61 (12–179) months. Characteristics of the population and the tumors were [median, (min–max)] age 57 (25–84) years old, tumor size 43 mm (20–280), RENAL score 7 (4–12), PADUA score 8 (5–14). Treatments were 55% partial nephrectomy, 45% radical nephrectomy, 74% open surgery, and 26% laparoscopy. In pathological report, cystic RCC were mainly of low grade (1–2, 77%) and low stage (pT1, 81%). The two main histological subtypes were conventional (56%) and papillary (23%) RCC. Staging at presentation and histological characteristics were similar between Bosniak III and IV, except for high grade which was more common in Bosniak IV (12 vs 36%, p < 0.01). The Bosniak classification was not predictive of the recurrence, as 5- and 10-year disease-free survival were similar in Bosniak III and IV (92% vs 92% and 84% vs 83%, p = 0.60). Conclusion: The Bosniak classification is predictive of the risk of malignancy but not of the oncological prognosis. Regardless of the initial Bosniak categories, almost all cystic RCCs were of low stage/grade and had low long-term recurrence rate.