Interstage colorectal cancer is defined as colorectal cancer (CRC) that is not detected in a colorectal screening program and is detected before the next recommended screening date. The interstage CRC detection rate is a strong indicator to assess the quality and effectiveness of CRC screening programs. an article by Dr. Chiu et al. published in the journal Gut in October 2015 indicated that one of the important indicators affecting the interstage CRC detection rate in colorectal cancer screening programs in the Taiwanese population is the results of the biennial fecal immunobiochemical test (FIT). The investigators analyzed the detection rate of interstitial CRC at colorectal microscopy in FIT-positive participants and concluded that the majority of interstitial cancers probably originated from lesions missed during colorectal microscopy. Fecal hemoglobin concentration was also an independent predictor of interstitial cancer. The clinical significance and value of this article is reviewed by Prof. Dekker et al. from the University of Amsterdam Medical School and published in a recent issue of Natrue Reviews: Gastroenterology & Hepatology. The primary goal of CRC screening programs is to reduce long-term mortality associated with CRC. Although colonoscopy is the gold standard for the detection and prevention of CRC and progressive adenomas, it is a risky and invasive test that is not widely performed in many countries, requiring us to further discover more convenient and appropriate methods for CRC screening. FIT is a non-invasive test that is relatively inexpensive and widely available. Although less sensitive than colorectal microscopy, FIT can screen for people at high risk of CRC from the general population and further refine endoscopy. The FIT-positive population has a higher prevalence of CRC and/or progressive adenomas (together, progressive neoplasms) and, therefore, a higher rate of CRC detection at follow-up. To ensure the validity of the CRC screening program, all lesions in the colorectum should be detected and completely removed by endoscopic polypectomy or surgery. In the FIT screening program, interstitial carcinoma can be detected not only initially from screening tests but also endoscopically in FIT-positive patients. The sensitivity of FIT ranges from 75% to 88%, and the fecal hemoglobin concentration detected by FIT is positively correlated with the sensitivity of detecting progressive tumors. The results of studies on the detection rate of CRC by colonoscopy vary, however, the main influencing factors are consistent: missed detection of CRC or progressive adenomas, incomplete excision of the lesion, and the growth and progression of tumor tissue due to specific pathological factors. Many past studies have concluded that interstage cancer is primarily associated with the first two factors, with the quality of endoscopy being the most important. A landmark study in Poland proposed a clear relationship between adenoma detection rate and the incidence of interstitial carcinoma. The Taiwan Population CRC Screening Program began in 2004 to provide biennial FIT examinations for people aged 50 to 69 years. This cohort study included 29,969 individuals who were screened positive for FIT from 2004 to 2009 and who were not found to have CRC by complete colonoscopy after each round of screening. This universal tumor registry had a high coverage rate of 98.6%. The risk of CRC was increased when the endoscopic adenoma detection rate was less than 15% and fecal hemoglobin concentrations were high (≥150ug Hb/g). The investigators concluded that poor quality of endoscopy was a major factor in the development of interstitial carcinoma, while fecal hemoglobin concentration was an independent predictor. Therefore, the screening program has two interventions to reduce the incidence of interstitial cancer: improving endoscopy quality and accounting for FIT results in the assignment (e.g., assigning high fecal hemoglobin concentrations to high-quality endoscopy centers or providing a second follow-up endoscopy if the first endoscopy is negative/endoscopy quality is poor). The most important factor in improving the effectiveness of screening examinations is the quality of colonoscopy. The study by Dr. Chiu et al. provides a content framework for prospective data on the incidence of screening for interstitial cancers around the world, namely how to systematically analyze and address factors affecting interstitial cancers to maximize the effectiveness of screening programs.