Toward a molecular genetic classification of clear cell renal cell carcinoma.
341 Background: Clear cell renal cell carcinoma (ccRCC) displays a variety of clinical behaviors. However, the molecular underpinnings are unknown. We discovered that BAP1 is mutated in approximately 15% of ccRCC and that BAP1 and PBRM1mutations are largely mutually exclusive. Herein, we investigate the clinicopathological significance of these molecular subtypes. Methods: Tumors from 145 patients with primary ccRCC were sequenced for PBRM1 and BAP1. Tumors were classified into BAP1-mutated and those exclusively mutated for PBRM1. Tumors were evaluated for pathologic features, gene expression and associated outcomes. A second independent cohort (n=327) from The Cancer Genome Atlas (TCGA) was used for validation. Results: When compared to PBRM1-mutant tumors, BAP1-mutant tumors were associated with aggressive pathological features including high Fuhrman grade and tumor necrosis. BAP1-mutant and PBRM1-mutant tumors exhibited distinct gene expression signatures. The median overall survival (OS) was shorter for patients with BAP1-mutant tumors (4.6 years; 95% CI, 2.1-7.2), than for patients with PBRM1-mutant tumors (10.6 years; 95% CI, 9.8-11.5), corresponding to a hazard ratio (HR) of 2.7 (95% CI, 0.99-7.6, p = 0.044). A similar HR was observed in the independent dataset from the TCGA (2.8; 95% CI, 1.4-5.9; p = 0.004). The BAP1-mutant group could be further subdivided into tumors with mutations exclusively in BAP1 and those with mutations in both BAP1 and PBRM1. Double mutant tumors constituted a minority (n = 4; in TCGA), and were associated with the shortest OS (HR, 10; 95% CI, 3.2-33.6). Conclusions: Our findings reveal novel biological subgroups of ccRCC with distinct clinical outcomes, a high-risk BAP1-mutant group and a favorable PBRM1-mutant group. These data establish the basis for a molecular subclassification of ccRCC that could influence treatment decisions in the future.