Our study will enroll consecutive subjects participating in the health check-up at National Taiwan University Hospital (Health Management Center), who will undergo a standard protocol, including I-FOBT, G-FOBT, HpSA, face-to-face interviews, blood chemistries, colonoscopy and EGD. Prior to the examination, a self-administered questionnaire will be used to collect information on participants' demographics, social habits, clinical symptoms, and medical/medication histories. To ensure that our study population was asymptomatic and the bleeders were occult, we excluded those who had overt GI symptoms and overt GI bleeding from analyses. During the same period, patients with screening detected GI tract cancers from other screening sites, such as throat cancer, esophageal cancer, gastric cancer, and colorectal cancers, will also be invited to participated in the study. This enrollment was based on insufficient GI cancer case number in the interim analyses based on a single screening site.