Results of screening, rescreening, and follow-up in a prospective randomized study for detection of colorectal cancer by fecal occult blood testing. Results for 68,308 subjects.

All 68,308 inhabitants of Göteborg born between 1918 and 1931 were randomly divided into a test and a control group. The subjects in the test group were invited to perform Hemoccult II fecal occult blood testing on 3 days and to repeat the test after 16 to 24 months. In the prevalence screening 21,347 (63%) performed the test, and in the rescreening 19,991 (60%). Investigation of the 942 (4.4%) with positive tests in the prevalence screening showed 47 cancers and 129 subjects with adenomas > or = 1.0 cm. In the rescreening 5.1% had a positive test, and 34 cancers and 122 subjects with adenomas (> or = 1.0 cm) were found among those. Cancer had also been diagnosed in 19 subjects in the interval between the two screening occasions and in 15 subjects among the non-responders. Forty-four cancers had been diagnosed in the control group during the same period. Cancers detected by screening were at a less advanced stage than in the control group. It is too early to show any effect of screening on mortality from colorectal cancer.