Abstract
Aim: There have been few reports on interval colorectal cancer in persons undergoing screening by the immunochemical fecal occult blood test (iFOBT). We investigated the characteristics of interval colorectal cancer among participants in an iFOBT screening program. Methods: Interval colorectal cancer was defined as invasive cancer diagnosed by another test within the next fiscal year after a negative iFOBT, while positive colorectal cancer was defined as invasive cancer diagnosed by screening or another test within the next fiscal year after a positive iFOBT. The gender, age, screening history, stage, location, and histological features were compared between interval cancer and positive cancer, and cluster analysis was performed to classify interval cancer. Medical records of the subjects were linked with data on confirmed colorectal cancers from the Gunma Cancer Registry to identify interval and positive cancers. Results: Among 27,799 persons undergoing iFOBT, 10 interval cancers and 69 positive cancers were detected. Ninety percent of interval cancers were detected by annual screening. Persons with interval cancer were more likely to be female and elderly than that those with positive cancer. Interval cancers were significantly more likely to be of higher stage and to involve the cecum compared with positive cancers. Cluster analysis identified two clusters of interval cancers, which were “Elderly Advanced Right Colon” and “Non-elderly Rectal.” Conclusions: Interval cancer showed characteristic features with respect to gender, age, location, and stage. iFOBT appears to be less effective for detecting cancer of the right colon in elderly persons.
