CUA 2017: Cystic Renal Masses: Is the Bosniak Classification System an Adequate Predictor of Survival?

Toronoto, Ontario ( Dr. Thenappan Chandrasekar and colleagues presented their assessment of cystic renal masses and implications of the Bosniak classification system at this morning’s GU oncology poster session at the CUA 2017 annual meeting. Previous studies have suggested that although malignancy rates may be >50%, mortality rates from these lesions are quite low.1,2 The objective of this study was to evaluate intervention rates and survival outcomes of complex renal cysts in a single-center (University Health Network, Toronto) experience. 

For this study, between 2001 and 2013, a radiology database was queried to identify all cases of complex cysts (n=336). Primary outcomes were metastases-free survival (MFS), cancer-specific survival (CSS), and overall survival (OS). Secondary outcomes included radiographic or clinical progression, renal biopsy pathology and rate of surgical/ablative intervention.  Among these 336 patients, 185 (55%) were Bosniak IIF, 122 (36%) were Bosniak III, and 29 (9%) were Bosniak IV cysts. Over a median follow-up of 74 months, MFS was 99.1%, CSS was 99.7% and OS was 93.8%. For the 38 patients that underwent percutaneous biopsy of a solid component within the cyst, 13 patients were found to have renal cell carcinoma (RCC). Specific to interventions, 65 patients underwent surgery/ablations, including 35% undergoing radical nephrectomy, 57% partial nephrectomy and 8% ablation with a median time to intervention of 6.1 months. Among patients with final pathology, 5% were benign and the remainder were RCC: 45% clear cell, 20% multilocular cystic, 15% papillary type I, 3% papillary type II, 2% de-differentiated, 1% chromophobe, and 1% tubulocystic. For patients monitored on surveillance, radiographic upstaging was rare (2-3%) with no Bosniak III  IV upstaging. 

In summary, cancer-specific and overall survival for patients diagnosed with Bosniak IIF-IV complex renal cysts is low, in line with previously published studies. Even in the group that received no intervention, CSS was excellent. The authors conclude that given the indolent clinical course of these lesions, there should be reconsideration of management guidelines for complex renal cysts based on Bosniak classification. Particularly for Bosniak III cysts, active surveillance may be a reasonable alternative.

Presented By: Thenappan Chandrasekar, MD, University of Toronto, Toronto, ON, Canada

Written By: Zachary Klaassen, MD, Urologic Oncology Fellow, University of Toronto, Princess Margaret Cancer Centre  Twitter: @zklaassen_md at the  72nd Canadian Urological Association Annual Meeting - June 24 - 27, 2017 - Toronto, Ontario, Canada

1. Smith AD, Remer EM, Cox KL, et al. Bosniak category IIF and III cystic renal lesions: outcomes and associations. Radiology 2012 Jan;262(1):152-160.

2. El-Mokadem I, Budak M, Pillai S, et al. Progression, interobserver agreement, and malignancy rate in complex renal cysts (≥ Bosniak category IIF). Urol Oncol 2014 Jan;32(1):24.e21-e27.