OR51E2 and prostate neoplasm: GPR133, GPR134, GPR135, GPR136, and GPR137 are highly homologous in the prostate-specific GPR-encoding gene (PSGR) [16], whose expression in prostate tissue is restricted, but much higher in prostate tumor than in normal tissue, so it can be inferred that PSGR may act as an important gene in the development and progression of early prostate cancer [17].