For people who have been identified as being at higher risk of developing colorectal cancer, a screening programme that uses colonoscopy appears to be less efficient than using faecal occult blood tests, French researchers report at ESMO 2014.

Dr Sylvain Manfredi from CHU Pontchaillou in Rennes, France, and colleagues conducted their study in a region of the country where faecal occult blood test (FOBT) screening for people with average risk of colorectal cancer has been implemented for long time.

As part of the screening program, a pre-screening procedure is undertaken by a general practitioner or gastroenterologist to identify patients who are at higher than average risk of colorectal cancer based on their family history.

Those patients were invited to undergo colonoscopy rather than FOBT.

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 that is 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 1179 patients studied, 889 underwent colonoscopy, the researchers report.

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 to the positive predictive value in the average risk population selected by a positive FOBT, they say.

In this population, the positive predictive value of the colonoscopy done after positive test 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 faecal 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.

“In the study from Manfredi, it was shown that a prediction for screening colonoscopy using high risk features – based on family history – revealed a less positive predictive value than pre-screening by FOBT with follow-up of those who have a positive result,” Schmoll said.

“These data favour the widely used standard approach of routine use of FOBT followed by colonoscopy only when the FOBT test is positive, rather than colonoscopy first. Those patients with prior FOBT are at higher risk for having cancer or precursor lesion compared to those who are only identified by family history,” Schmoll said.

“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. FOBT can be negative in a number of patients despite the presence of adenoma, precursor lesions or even in early cancer. Therefore the optimal method remains the colonoscopy in all patients,” Schmoll said.

“The data support the use of both options as part of a large national screening programme which is adapted to several different groups, to optimise the outcome and increase the rate of cure,” Schmoll noted.

Source: ESMO