Long-Term Outcomes of Patients With Low Grade Cystic Renal Epithelial Neoplasms

Objective: To report on the long-term oncologic outcomes of 3 subtypes of low grade cystic renal epithelial neoplasms—multilocular cystic neoplasm of low malignant potential (MCLMP), cystic clear cell RCC (ccRCC), and cystic clear cell papillary RCC (ccpRCC), following 2016 reorganization by the World Health Organization. Materials and Methods: A total of 3865 patients underwent radical or partial nephrectomy for unilateral, sporadic ccRCC between 1970 and 2010, of which 145 had previously been classified as cystic ccRCC. One genitourinary pathologist, blinded to outcome, rereviewed and reclassified the specimens by 2016 WHO criteria. Oncologic outcomes were estimated using the Kaplan-Meier method. Results: Of 145 specimens, 18 (12%) were classified as MCLMP, 95 (66%) cystic ccRCC, and 32 (22%) cystic ccpRCC. Those with MCLMP were more likely female (61% vs 29% vs 31%, P = .03) with larger tumors (median 4.6 cm vs 3.0 cm vs 2.3 cm, P = .02) compared to those with cystic ccRCC and cystic ccpRCC, respectively. Only 2% of cystic ccRCC had tumor necrosis or grade 3 nucleoli present. Median follow-up for survivors was 10.3 years (interquartile range 7.4-14.9). Overall, 1 MCLMP, 5 cystic ccRCC, and 4 ccpRCC recurred during follow-up. Ten- and 20-year cancer-specific survival was 100% across all subtypes. Conclusion: In a large cohort of patients previously classified as cystic ccRCC with pathologic rereview and long-term follow-up, we noted that MCLMP is the least common subtype of low grade cystic renal epithelial neoplasms. Regardless, all subtypes are associated with an excellent long-term prognosis following surgical resection.