GPR137 and prostate cancer: As one of the novel human GPCRs that play a vital role in cell signaling transduction, recently studies have identified that GPR137 expression is closely associated with cancer and the aberrantly up-regulated expression of GPR137 is correlated with carcinogenesis in kinds of cancers, such as prostate cancer [6], ovarian cancer [8], pancreatic cancer [9] as well as osteosarcoma [10], indicating the potential role of GPR137 as a novel tumor biomarker.