Purpose: To evaluate and compare pathological characteristics of renal cysts Bosniak IIF, III and IV in light of recent histological classification.
Patients and methods: The French research network for kidney cancer UroCCR conducted a multicentre study on patients treated surgically for a renal cyst between 2007 and 2016. Independent radiological and centralized pathological reviews were performed for every patient. Pathological characteristics were compared to the Bosniak classification.
Results: Of a total 216 patients included, 175 (81.0%) tumours (90.9% of Bosniak IV, 69.8% of Bosniak III) were malignant or had a low malignant potential, with 60% of clear cell renal cell carcinoma (CCRCC), 24% of papillary RCC (PRCC) and 6.9% of multilocular cystic renal tumour of low malignant potential (MCRTLMP). Malignancies were mostly of low pT stage (86.4% of pT1-2), and low ISUP grade (68.0% of 1-2). Bosniak III cysts had a lower rate of CCRCC (46.7 vs. 67.3%), higher rate of PRCC (30 vs. 20.9%) and MCRTLMP (18.3 vs. 0.9%) compared to Bosniak IV (p < 0.001). Low-malignant potential lesions were less likely Bosniak IV and pT3-4 stage was more frequent in Bosniak IV vs. III (15.7 vs. 3.5%; p = 0.04). There were two recurrences (1.1%) and no cancer-related death occurred during follow-up.
Conclusion: These results confirmed that cystic renal malignancies have excellent prognosis. Bosniak III cysts had a low malignant potential, which suggests surveillance could be an option for these lesions.
Keywords: Bosniak classification; Computed tomography; Histology; Low malignant potential; Renal cell carcinoma; Renal cysts.