Colorectal cancer following negative colonoscopy: is 5-year screening the correct interval to recommend?

BACKGROUND: Despite the high sensitivity of screening colonoscopy, polyps and cancers can still go undetected. With the polyp-to-cancer transformation cycle averaging 7-10 years, present guidelines recommend repeat colonoscopy within 10 years after negative screening. However, not all colorectal malignancies follow this decade-long progression. This study evaluates the incidence and pathology of colorectal cancers following a previous negative screening colonoscopy.
METHODS: Records of patients who underwent a colectomy at our institution, from 1998 to 2009, were reviewed retrospectively. A total of 1,784 patient records were screened using exclusion criteria for inclusion in this study. The patients were divided as follows: Group 1 included patients with a negative colonoscopy within the previous 5 years; Group 2 included patients without a previous colonoscopy or with a previous colonoscopy more than 5 years prior. Group 1 patients were evaluated by colonoscopy for anemia, diverticulitis, signs of obstruction, and bleeding. Age, tumor location, operation performed, and pathology findings were recorded. The χ(2) test and paired t test were used for statistical analysis.
RESULTS: A total of 233 patients were included in this study. Group 1 contained 43 patients with a mean age of 73 years (range = 35-94, median = 75). Group 2 had 190 patients with a mean age of 68 years (range = 19-91, median = 70). Group 1 consisted of 18 male and 25 female patients, and Group 2 included 94 male and 96 female patients. Both groups were further classified into the following age categories: <50 years, 50-80 years, and >80 years. Eighteen percent of the total study population had newly discovered colorectal cancer within a 5-year colonoscopy screening period. There were no significant differences in the distribution of the T and N stages between the two groups and no statistically significant differences when the rate of lymphovascular invasion (19 vs. 17 %; p = 0.39) and perineural invasion (7 vs. 11 %; p = 0.58) were compared.
CONCLUSIONS: Within 5 years, 18 % of our study population developed colorectal cancer. Most of these malignancies were found within the 50-80-year age group and located predominantly in the right colon and distally in the sigmoid and rectum. While distal cancers may be visualized by flexible sigmoidoscopy, those located more proximally may be missed, necessitating the need for a full colonoscopy. Although staging was similar between the two groups, Group 1 tumors were less aggressive despite having appeared within 5 years. As a result of our incidence of colorectal cancer within a 5-year interval, a shorter period for routine colonoscopy may be considered.