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There is sufficient evidence that sigmoidoscopy, colonoscopy, and stool-based screening reduce deaths from colorectal cancer, a report from the International Agency for Research on Cancer (IARC) stated.

The relative risk of death from colorectal cancer was lower -- from 9% to 40% depending on method used -- among screened individuals, reported Béatrice Lauby‑Secretan, PhD, of the IARC in Lyon, France, and colleagues in the .

"There is also sufficient evidence that, for these techniques, the benefits outweigh the harms," Lauby‑Secretan told 澳门老奇人论坛.

The IARC reviewed six screening methods -- three stool-based tests for occult blood, sigmoidoscopy, colonoscopy, and CT colonography -- to evaluate their impact on colorectal cancer incidence and mortality reduction as well as whether the benefits with each outweighed the harms.

Harms associated with colorectal cancer screening can include psychological harms from false positives as well as unnecessary follow-up endoscopies that, while uncommon, also carry risks of bleeding and perforation. With CT colonography, potential harms also include radiation-induced effects.

In randomized trials of stool-based screening, the relative risk of death from colorectal cancer in individuals who received guaiac testing plus colonoscopy following a positive test, was significantly lower than unscreened controls -- 9% to 14% lower with guaiac testing without rehydration every 2 years, and 16% to 32% lower with higher-sensitivity guaiac testing every 1 or 2 years.

And while fecal immunochemical testing (FIT) for high-risk colon cancer has shown mixed results, the IARC determined there was sufficient evidence for mortality reduction with FIT screening every 2 years. In three cohort studies, individuals screened with FIT had lower relative risks of death from colorectal cancer than unscreened patients in the order of 10% to 40%. The report noted that a variety of FIT tests are available, with a wide range of sensitivity and specificity among them.

For sigmoidoscopy screening, three of four randomized trials showed a 22% to 31% lower relative risk of death from colorectal cancer. As no randomized trials to date have data for colonoscopy screening, the authors reviewed a large number of observational studies conducted in a screening setting.

Sigmoidoscopy and colonoscopy also had "sufficient" evidence for reducing colorectal cancer incidence, according to IARC. Evidence for reducing incidence was either limited or suggested a lack of effect for stool-based tests.

"It is worth noting that the evidence for CT colonography in reducing colorectal cancer incidence or mortality was limited," said Lauby‑Secretan.

In a randomized trial of CT colonography versus colonoscopy, colorectal cancer was found at similar rates, but the CT colonography performed worse when it came to advanced adenomas (5.6% versus 8.2%) and advanced adenomas 1 cm or larger (5.4% versus 6.3%).

The majority of studies reviewed included asymptomatic individuals -- typically ages 50 to 70 -- at average risk for colorectal cancer. "The evaluations must be considered in a context of high-quality screening, and when follow-up and treatment are ensured," said Lauby‑Secretan.

Missing from the report is discussion of participation with the various screening methods. Rates of screening with colonoscopy (58.2% in 2013, according the National Cancer Institute) are far lower than those for cervical and breast cancers (80.7% and 72.6%, respectively).

The IARC reviewed literature on this subject, and on trials assessing ways to improve participation, but the data were not included in the evaluation. "Similarly, modeling studies of cost-effectiveness were reviewed but not evaluated," said Lauby‑Secretan.

The authors attempted to compare the effectiveness of the different screening techniques, but the evidence was inconclusive. One meta-analysis found that sigmoidoscopy was better than guaiac testing in reducing colorectal cancer incidence, while another favored colonoscopy over both sigmoidoscopy and guaiac testing for reducing deaths from colorectal cancer.

"This is a very nice review," Harminder Singh, MD, of the University of Manitoba in Winnipeg, told 澳门老奇人论坛.

Singh, who was not involved in the report, highlighted that "only relative reductions are discussed and not the absolute benefits," noting that by design the IARC authors did not perform a meta-analysis to synthesize the results, and therefore the report does not indicate the overall magnitude of effect for each modality.

"There is very little doubt screening for colon cancer reduces deaths from colon cancer in the appropriate age group," he said. "The incremental benefits, harms and overall costs of one screening test versus the other needs further study."

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