For people identified as being at higher risk of developing colorectal cancer, a screening program that uses colonoscopy appears to be less efficient than using fecal occult blood tests (FOBTs), French researchers reported at the European Society for Medical Oncology (ESMO) 2014 Congress in Madrid, Spain.
Sylvain Manfredi, MD, from CHU Pontchaillou in Rennes, France, and colleagues conducted their study in a region of the country where fecal occult blood test screening for people with average risk of colorectal cancer has been the practice for a long time.
As part of the screening program, a general practitioner or gastroenterologist uses a prescreening procedure to identify which patients may have higher than average risk of colorectal cancer based on their family history. Those patients were invited to undergo colonoscopy rather than FOBT.
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The aim of the study was to estimate the positive predictive value of colorectal neoplasia in this high-risk group. Positive predictive value is a statistical measure defined as the ratio of true positive results to the number of times the test shows a positive result (which can include true positive results and false positives, where the test indicates a positive result but the patient does not actually have colorectal cancer).
Of 1,179 patients studied, 889 underwent colonoscopy, the researchers reported. Overall, 253 colorectal neoplasias were diagnosed including 35 cancers and adenomas (polyps) in 219 patients. A total of 209 advanced adenomas were diagnosed.
The authors calculated that the positive predictive value of colonoscopy was 3.9% for cancer, 12.9% for advanced adenoma, and 25% for adenoma overall.
This compared poorly with the positive predictive value in the average risk population selected by a positive FOBT. In this population, the positive predictive value of colonoscopy after a positive FOBT in their administrative area ranges from 7.5% to 10% for cancer, from 15% to 27% for advanced adenoma, and between 32% and 37% for adenoma.
“The take-home message is that the positive predictive value for colorectal neoplasia in high risk patients screened by colonoscopy is lower than it is for average risk patients screened by FOBT.”
“As a result, we believe this population may benefit from fecal occult blood or immunochemical blood testing to select the best candidates for colonoscopy.” Further studies are required to understand how best this could be achieved, Manfredi said.
“These data favor the widely used standard approach of routine use of FOBT followed by colonoscopy only when the FOBT test is positive, rather than colonoscopy first. However, if colonoscopy is restricted only to those patients who have positive FOBT, there is a high chance that adenoma or even cancer can be not identified. Therefore the optimal method remains the colonoscopy in all patients,” commented Professor Hans-Joachim Schmoll, MD, PhD, former head of the Division of Hematology and Oncology and director of the Center for Cell and Gene Therapy, Martin Luther University, Halle, Germany and professor of medicine at Martin Luther University, Germany.
