Screening reduces colorectal cancer death not development risk

By Lauretta Ihonor

Screening for colorectal cancer (CRC) by testing for fecal occult blood (FOB) reduces the risk for death from this type of cancer, study results show.

"Screening for CRC should show a reduction in CRC mortality and a reduction in the incidence of CRC as a consequence of removing large adenomas in the screened population," say John Scholefield (University Hospital, Nottingham, UK) and colleagues.

But they found that CRC development was unaffected by the implementation of a FOB-based CRC screening program.

In a commentary accompanying the article in Gut, Graeme Young (Flinders University, Adelaide, Australia) and colleagues say: "Current evidence makes it clear that using [guaiac based fecal occult blood test] for screening is a choice for a less effective test.

"This is why the European Guidelines for CRC Screening now recommend the use of [fecal immunochemical test for hemoglobin]."

The study involved the observation of CRC development and mortality rates among 151,975 UK individuals aged 45-74 years over a median follow-up period of 19.5 years. Participants were randomly allocated to undergo screening via FOB (n=76,056) or no screening (n=75,919; controls).

Those in the screening group received three to five invitations for repeat screening during the follow-up period. All underwent further investigation (colonoscopy) and appropriate treatment if a positive FOB test was obtained at any time.

Adenomas identified on further investigation were removed as these benign tumors are known to become malignant if left to grow, explain Scholefield et al.

In all, 2279 and 2354 people in the screening and control groups, respectively, developed CRC during the follow-up period. There was no significant difference between the groups, despite the removal of 615 adenomas larger than 10 mm from patients in the screening group.

In the screening group, only 236 CRC cases were detected by actual screening. The remaining cases of CRC among the group were identified between screenings or during follow-up protocols for colorectal adenomas identified by screening.

The findings revealed that most (71%) screen-detected cancers were Dukes' stage A or B tumour.

Scholefield et al report that a 13% reduction in CRC mortality was seen in the screening group compared with the control group, over the follow-up period.

They conclude that "screening by the FOB test is worthwhile because it reduces mortality from a common cancer," but note that "CRC screening is likely to continue to develop using newer tests such as immunological FOB testing."

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