[The incidence of malignant transformation of renal cysts of category 1, 2, and 2F by the BOSNIAK classification into multilocular cystic renal cell carcinoma].

RELEVANCE: Renal cysts remain the most common of benign renal lesions, but current literature is lacking large observational studies on the incidence of their malignant transformation. AIM: To assess the incidence of malignant transformation of renal cysts of category 1, 2, and 2F by the Bosniak classification into multilocular cystic renal cell carcinoma. MATERIALS AND METHODS: From January 2009 to December 2017, 177 patients with renal cysts of category 1 (n=50), 2 (n=74), and 2F (n=53) underwent laparoscopic decortication. In 10 cases, post-operative histological and immunohistochemical studies revealed foci of grade 1 (pT1a) multilocular cystic renal cell carcinoma. RESULTS: Foci of grade 1 (pT1a) multilocular cystic renal cell carcinoma were detected in 10 (5.65%) patients (five men, five women, mean age 58.9 years). The incidence of malignant transformation of renal cysts of categories 1, 2, and 2F was 0%, 2.7% (2 of 74 patients), and 15.1% (8 of 53 patients), respectively. Subsequently, all ten patients were submitted to surgical treatment: eight of them underwent a partial nephrectomy, and two received a nephrectomy. During a median of 49.3 (31-72) months follow-up, no metastasis, and recurrence of multilocular cystic RCC were observed. CONCLUSION: A more modern algorithm for managing patients with Bosniak category 1, 2 and 2F cysts need to be developed to establish early surveillance of patients starting with category 1 cysts. Given the low malignant potential of these tumors, they should be treated with organ-sparing surgery.