Follow-up after screening for colorectal neoplasms with fecal occult blood testing in a controlled trial

The aim of this study was to investigate the number of new colorectal neoplasms during the first seven years after the end of rescreening in a prospective randomized screening study.

27,700 inhabitants of Göteborg born between 1918 and 1922 (60-64 years old) who were randomly allocated to a control or a test group in 1982 were followed up. All people in the latter group were offered six fecal occult blood tests and rescreening 16 to 22 months later.

One hundred one carcinomas were diagnosed in the screened group and 128 in the control group during the seven years of follow-up. The number of carcinomas in the test group was half that in the control group during the first two years of follow-up, but equal during the rest of the follow-up period. The distribution of carcinomas according to Dukes classification was significantly better among the participants compared with the refusers (P < 0.02) but there was no difference in the Dukes distribution when the test and control groups as a whole were compared. The number of adenomas in the two groups during seven years of follow-up was the same.

The results indicate that screening and rescreening of a population has little influence upon the stage of the carcinomas in the test group compared with a control group during the first seven years of follow-up. The number of carcinomas was higher in the control than in the test group during the follow-up, probably because of a lead time effect during the screening.