Invasive colorectal cancer within 5 years of negative colonoscopy in a Japanese population

Aim Colonoscopy provides imperfect protection against colorectal cancer (CRC). In an attempt to improve cancer detection we evaluated the clinical features of invasive CRC detected within 5 years of a negative colonoscopy. Method The details of colonoscopies performed in a rural hospital in Japan were prospectively recorded at the time of the examination. The patients were followed over 5 years for the subsequent occurrence of cancer. Results In a 5-year period, 10 148 patients underwent colonoscopy and 202 without previous colonoscopy were diagnosed with invasive CRC. Of 3212 patients with a colonoscopy negative for cancer, nine developed invasive cancer within 5 years. The ratios for invasive CRC detected without/with previous colonoscopy were 60:1 in the rectum, 54:1 in the sigmoid colon, 15:1 in the descending colon, 28:0 in the transverse colon, 31:5 in the ascending colon and 14:1 in the caecum (P = 0.041). The ratio between left- and right-sided colonic cancer was also significantly different (129:3 and 45:6, P = 0.0078). Six (67%) of the invasive CRCs were in the ascending colon or caecum. Five of six patients with invasive CRC in the ascending colon and caecum had right-sided small adenomas at prior colonoscopy. Conclusion The majority of early/missed CRCs were right-sided and associated with prior right-sided colonic adenomas. Repeated colonoscopy of patients with right-sided adenomas at a shorter surveillance interval deserves consideration.