The efficacy of the guaiac fecal occult blood test (gFOBT) for colorectal cancer (CRC) screening has been proven by four randomized controlled trials (RCT) on gFOBT1–4 and three service screening programs on the fecal immunological test (FIT)5–7 but there still exists large uncertainty of overdiagnosis8, which is one of the demerits of population-based service screening that has already been noted in the PSA (prostate-specific antigen)9–11. The gene discussed is KLK3; the disease is colorectal cancer.