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

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.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.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.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.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.