The Importance of Lesion Size as an Indicator of Malignancy in Bosniak Category 3 Cystic Renal Masses

Objective: To evaluate the relationship between lesion size and malignancy rates in surgically removed Bosniak 3 renal cysts. Material and Methods: Patients who underwent radical / partial nephrectomy for cystic renal mass between January 2010 and December 2018 were retrospectively analyzed. Fifty two patients who were diagnosed as Bosniak 3 renal cyst in preoperative computed tomography (CT) and / or Magnetic Resonance Imaging (MRI) images were included in the study. ROC Curve analysis was performed among Bosniak 3 lesions and tumor size cut-off value predicting malignancy was found. Patients with tumor size below and above this value were compared in terms of patient characteristics and histopathological data. Results: The mean patient age was 54.2 ± 13.1 years and the mean follow-up period was 39.9 ± 25.2 months. The malignancy rate for all Bosniak 3 lesions was 63.5%. Male gender and low tumor size were correlated with malignancy in both univariate and multivariate analysis in comparison of patients with malignant and benign pathology. In the ROC Curve analysis, the cut-off value of the cyst, which predicted malignancy, was 45 mm (AUC = 0.735, p = 0.005). Patients were divided into two groups according to tumor size ≤45 mm (Group 1) and > 45 mm (Group 2). The malignancy rate was 77.8% and 48% in Group 1 and 2, respectively (p = 0.026, OR: 0.26, CI: 0.079-0.875). Conclusion: In Bosniak 3 renal cysts, low tumor size was found to be associated with malignancy.