Fecal Occult Blood Test

There are five controlled clinical trials that have been completed or that are in progress to evaluate the efficacy of screening utilizing the fecal occult blood test (FOBT). The Swedish trial is a targeted study for the group aged 60 to 64 years.[1] The English program selects candidates from lists of family practitioners.[2] The Danish trial offers screening to a population aged 45 to 75 years randomly assigned to a control and a study group.[3,4] The Memorial Sloan-Kettering Cancer Center-Strang Clinic (MSKCC) trial, completed in 1985, was an evaluation of the FOBT as a supplement to annual rigid sigmoidoscopy.[5] The study and control groups were selected by calendar periods.

The Minnesota trial demonstrated that annual FOBT testing using primarily rehydrated samples decreased mortality from CRC by 33% [6] and that biennial testing developed a 21% relative mortality reduction.[7] A large part of the reduction may be attributed to chance detection of cancer by colonoscopies; rehydration of guaiac test slides greatly increased positivity and consequently increased the number of colonoscopies performed. Subsequent analyses by the Minnesota investigators using mathematical modeling suggested that for 75% to 84% of the patients mortality reduction was achieved because of sensitive detection of CRCs by the test; chance detection played a minor role (16%-25% of the reduction). Nearly 85% of patients with a positive test underwent diagnostic procedures that included colonoscopy or double-contrast barium enema plus flexible sigmoidoscopy (FS). After 18 years of follow-up, the incidence of CRC was reduced by 20% in the annually screened arm and 17% in the biennially screened arm.

The English trial allocated approximately 76,000 individuals to each arm. Those in the screened arm were offered nonrehydrated FOBT testing every 2 years for three to six rounds from 1985 to 1995. Median follow-up time was 7.8 years. Sixty percent completed at least one test; 38% completed all tests. Cumulative incidence of CRC was similar in both arms. The trial reported a relative risk reduction of 15% in CRC mortality (odds ratio [OR] = 0.85; 95% confidence interval [CI], 0.74-0.98).[11] In this study, the serious complication rate of colonoscopy was 0.5 %. There were five deaths within 30 days of surgery for screen-detected CRC or adenoma out of a total of 75,253 individuals screened. After a median follow-up of 11.8 years, a difference in CRC incidence between the intervention and control groups was not observed. Overall, the disease-specific mortality-rate-ratio associated with screening was 0.87 (0.78-0.97, P = .01). The rate ratio for death from all causes was 1.00 (0.98-1.02, P = .79).[13]

The Danish trial in Funen, Denmark, entered approximately 31,000 individuals into each of two arms, in which individuals in the screened arm were offered nonrehydrated FOBT testing every 2 years for nine rounds over a 17-year period. Sixty-seven percent completed the first screen, and more than 90% of individuals invited to each subsequent screen underwent FOBT testing. This trial demonstrated an 18% reduction in CRC mortality at 10 years of follow-up,[14] 15% at 13 years of follow-up (relative risk [RR] = 0.85; 95% CI, 0.73-1.00),[15] and 11% at 17 years of follow-up (RR = 0.89; 95% CI, 0.78-1.01).[16] CRC incidence and overall mortality was virtually identical in both arms.