Fecal occult-blood testing (FOBT) and sigmoidoscopy have been recommended for screening for colorectal cancer, but the sensitivity of such combined testing for detecting neoplasia is uncertain.
Researchers have now warned however, that FOBTs for colon cancer may detect as few as 25% of abnormalities.
The report, published in the New England Journal of Medicine suggests that even a single sigmoidoscopy will identify just 70% of precancerous colon growths.
Colonoscopies were performed at 13 Veterans Affairs medical centers in the USA, to determine the prevalence of neoplasia and the sensitivity of one-time screening with a FOBT plus sigmoidoscopy.
Asymptomatic subjects (age range, 50 to 75 years) provided stool specimens on cards from 3 consecutive days. These samples were rehydrated and used for interpretation by FOBT.
Patients then underwent colonoscopy, with sigmoidoscopy defined as examination of the colon and sigmoid colon during colonoscopy.
Sensitivity was estimated by determining how many patients with an advanced neoplasia had an adenoma in the rectum or sigmoid colon.
Advanced colonic neoplasia was defined as an adenoma 10 mm or more in diameter, a villous adenoma, an adenoma with high-grade dysplasia, or invasive cancer.
A total of 2885 patients returned the three specimen cards for FOBT and underwent a complete colonoscopic examination.
Within this group, 24% of subjects with advanced neoplasia had a positive test for fecal occult-blood.
When compared to patients who had a negative FOBT, the relative risk of advanced neoplasia in subjects with a positive test was 3.47 (95% confidence interval 2.76 to 4.35).
Sigmoidoscopy identified 70% of all subjects with advanced neoplasia, while a combined one-time screening with a FOBT and sigmoidoscopy detected just under 76% of subjects with advanced neoplasia.
|Single FOBTs detected just 25% of abnormalities|
|N Engl J Med |
Researcher Dr David Lieberman, from the Portland Veterans Affairs Medical Center, Oregon, USA, said there was a case for using colonoscopy as a primary screening tool because people would not need a repeat test for another decade.
Dr Lieberman said, "We want to emphasize that people who have these screenings need to go back at intervals for repeat testing.
"What happens in real life is that patients often get only one test and no follow-up. This study tells us physicians can't use that single negative test to reassure our patients and that people need to return for repeat testing in order for screening programs to be effective."