| [ Summary ] |
To elucidate the difference between colorectal cancers with positive and negative results on fecal occult blood tests (FOBT), we conducted 59,579 sets of FOBT and total colonoscopy on 19,482 Japanese from 1983 through 1999. The subjects consisted of 45,163 males and 14,416 females 20-88 years of age.
Fecal occult blood was judged by the reversed passive hemagglutination (RPHA) method, an immunological FOBT, conducted once just before colonoscopy on the same day. Colonoscopy was performed, irrespective of the results of FOBT. FOBT was positive in 2,830 cases (4.7%) of the total examinations. A total of 212 colorectal cancer cases were found, of which 39 cases were invasive beyond the submucosa, 34 were invasive within the submucosa, and 139 were carcinoma in situ. The sensitivity of FOBT was 40% for total cancers (FOBT positive:nagative=85:127), 74% for invasive cancers beyond the submucosa (29:10), 44% in invasive cancers within the submucosa (15:19), and 29% in carcinoma in situ (41:98). According to multivariate analysis, which evaluated the parameters of the subject's gender or age, the cancer's location, shape, size or depth of invasion, and accompanying adenomal quantity or size, the location and size of the lesions were both judged as significant factors for FOBT result. Small cancers located on the right side of the colon tended to be negative for FOBT. As to location, sensitivity of FOBT for all colorectal cancers was 38% in the rectum, 48% in the sigmoid, 44% in the decending, 20% in the transverse, 44% in the ascending colon, and 33% in the cecum, respectively. As to size, the sensitivity of FOBT was 3% for those which were <10mm, 29% in 10 -19mm, 50% in 20-29mm, and 79% in >=30mm, respectively. Small invasive cancers on the right side of the colon presented a flat appearance in many cases. |