PBRM1 and nonpapillary renal cell carcinoma: Due to lack of paired normal controls and the limitation of WTS technology, the mutation frequencies for the vast majority of important ccRCC variant genes, such as VHL, BAP1 and SETD2, were shown in higher levels than in the TCGA cohort, except for PBRM1, a second most significantly mutated gene (SMG) (33.7% in the Caucasian population) as previously described [8, 42], which was observed with only 14.5% mutation rate in Chinese patients (Additional file 2: Table S1a).