MTR and nonpapillary renal cell carcinoma: Given the importance of this pathway in carcinogenesis, ethnic differences and the discrepancies in previous studies, the present case-control study was conducted to define the association between the one-carbon metabolism pathway genes polymorphisms and the ccRCC risk in Chinese population, through testing the polymorphism in six key genes (CBS, MTHFR, MTR, MTRR, SHMT1, and TYMS) in this pathway.