The incidence of post-colonoscopy colorectal cancer: a retrospective long-term cohort study using a colonoscopy database.

PURPOSE: The cumulative incidence of post-colonoscopy colorectal cancer remains unclear. Our aims were to estimate the incidence of and identify risk factors associated with post-colonoscopy colorectal cancer.
METHODS: We conducted a retrospective cohort study using the colonoscopy database of the Department of Gastroenterology, the University of Tokyo Hospital Records from1995-2012. A cohort of 2544 patients, who received multiple colonoscopies without colorectal cancer findings at first colonoscopy, was selected. The primary outcome was post-colonoscopy colorectal cancer; data were censored at the date of final colonoscopy. We assessed patients' background characteristics, colonoscopy findings, and cancer characteristics, including location and size. The cumulative incidence of colorectal cancer was evaluated, and a Cox proportional hazards model was used to estimate hazard ratios (HRs).
RESULTS: Colorectal cancer was identified in seven (0.77/1000 person-years) patients during the mean follow-up period of 3.6 years (maximum, 17 years). The cumulative incidence of colorectal cancer was 0, 0.47, 0.62, and 0.62% at 1, 5, 10, and 15 years, respectively. Cancer was identified in the rectum in five of seven patients. Polyp size >10 mm (HR 5.7, p = 0.023) and intubation time >30 min (HR 11.6, p = 0.003) at first colonoscopy were associated significantly with an increased incidence of post-colonoscopy colorectal cancer.
CONCLUSIONS: Although several factors were associated with an increased risk of post-colonoscopy colorectal cancer, the incidence of this disease might be low in patients who received at least twice colonoscopy. High proportion of rectal cancer in post-colonoscopy colorectal cancer should be noted.