Therefore, we hypothesized that polymorphisms of genes encoded cyclin-dependent kinase 4 and 6 (CDK4 and CDK6), cyclin D1 (CCND1), CDK inhibitors p16INK4a and p15INK4b, as well as the retinoblastoma protein (RB), could modulate prostate cancer risk and influence the corresponding mRNA levels. Here, CDK4 is linked to prostate cancer.