Colorectal cancer occurring in the interval between colonoscopies is called interval colorectal cancer, i.e., colorectal cancer occurring within 5 years after colonoscopy, and its causes can be classified as missed microscopy (e.g., flat tumors or <1 cm tumors), incomplete polypectomy lesions, or lesions of unknown origin. Therefore, Professor Samsadder et al. from the University of Utah Cancer Institute investigated the proportion, characteristics and risk factors of patients with interval colorectal cancer occurring within 6-60 months after undergoing colonoscopy. The study found that the occurrence of interval colorectal cancer may be due to the unique biological characteristics of this type of colorectal cancer and/or poorly managed colonoscopy surveillance. The study was recently published in the U.S. journal Gastroenterology. The researchers conducted a population-based cohort study of Utah residents who underwent colonoscopy between 1995 and 2009 at Intermountain Healthcare or the University of Utah Health Care System, which provided physical examinations for more than 85 percent of the state's residents. Because colonoscopy findings were correlated with their cancer history, patients who had undergone a colonoscopy in the 6-60 months prior to the diagnosis of interval cancer were screened from the Utah population database as the study population. Logistic regression was used to calculate the risk factors associated with the development of interval colorectal cancer. The results of the study showed that of 126,851 patients who underwent colonoscopy, 2,659 were diagnosed with colorectal cancer, and 6% of colorectal cancer patients (159 of 2,659) occurred within 6-60 months after colonoscopy. Gender and age were not associated with interval colorectal carcinogenesis. Patients with interval colorectal cancer had a higher and statistically significant rate of adenoma detection at colonoscopy (57.2%) compared to patients with colorectal cancer detected at colonoscopy (36%) or patients without cancer (26%). Patients with septal colorectal cancer were more likely to have a family history of colorectal cancer, with a 2.27 advantage ratio, and patients with septal colorectal cancer had a lower risk of death than patients with colorectal cancer detected at direct colonoscopy, with a hazard ratio of 0.63. The results of the above study suggest that septal cancer was present in 6% of patients in this population-based study and that septal colorectal cancer was associated with proximal colon, early cancer, low risk of death, high incidence of adenoma, and a family history of colorectal cancer. These findings suggest that the occurrence of septal cancer may be associated with the unique biology of colorectal cancer and/or poorly managed colonoscopic surveillance. From this study, it appears that the operative skills and treatment outcomes of the first-time colonoscopist may be key factors in the occurrence of septal colorectal cancer. To reduce the incidence of septal colorectal, in addition to regular and effective endoscopic surveillance, there should be an urgent need for enhanced training of endoscopists in the accurate examination and effective treatment of colorectal lesions.