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ACS: Start colorectal cancer screening at age 45

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Dr. John M. Inadomi, AGAF, of the University of Washington provides a perspective on the recommendation to start screening younger

The latest recommendations from the American Cancer Society added individuals 45 years and older to the population for whom CRC screeningshould be performed. The change from a start age of 50 was prompted by the increase in CRC reported in younger adults and was based on a computer simulation that predicted a greater number of life-years saved using an earlier age for initiation of screening among adults at average risk for development of colorectal cancer. It is likely that screening will reduce cancer mortality even in this younger age group; however, several issues should be considered when implementing this policy.

Differences in screening tests: The reason for the increase in CRC in younger adults is not known. Nor is it understood why this increase is far greater for rectal cancer than cancers more proximal in the colon. Based on this observation, however, it is possible that flexible sigmoidoscopy may be a more appropriate test than colonoscopy for younger adults. Conversely, we do not know if the precursor of early-age CRC is more likely to be a flat lesion that is more difficult to detect using endoscopy, or less likely to bleed that may make FIT less able to detect, or have a genetic mechanism different from proximal CRC that is not part of the current DNA stool testing.

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Dr. John M. Inadomi

The evidence supporting screening tests are not equal. No randomized trial confirming the effectiveness of screening colonoscopy to reduce CRC mortality has been completed, although at least four studies are ongoing. More importantly, a recent study of one-time screening flexible sigmoidoscopy published in JAMA reported a significant reduction in CRC incidence and mortality among men that was not seen among women. A variety of factors may have caused this observation, one of which is that the age-related incidence of CRC among women is lower compared with men. One-time screening will prevent fewer cancers in women since the majority of cancers precursors have not developed at a younger age. Starting screening at age 45 years may miss even more cancers among women.

Value is the benefit gained with screening compared with the resources required to implement screening. The value of screening is greater in older individuals than in younger individuals because the risk of CRC is increased and for this reason, population-based screening should focus on screening older adults who have not undergone screening. Unfortunately, U.S. population adherence to CRC screening remains below 70% with little improvement since 2010. Only after the older population is fully screened should our attention shift to younger populations.

Disparities: The individuals most likely to undergo screening are unlikely to be the individuals most likely to benefit. African Americans have a higher age-related incidence of CRC but have the lowest screening rates in the U.S. compared with other racial and ethnic groups. This relates to not only reduced access but also reduced utilization. It is a concern that, by increasing the pool of individuals recommended for screening, we may also reduce access to those who may benefit most.

The ACS recommendations to go low may reduce colorectal cancer mortality in younger adults; however, our lack of understanding about the biology of the cancer hampers our ability to recommend the optimal screening strategy, sacrifices value, and may increase disparities in cancer outcomes.

John M. Inadomi, MD, AGAF, is a Cyrus E. Rubin Professor of Medicine and head of the division of gastroenterology at the University of Washington School of Medicine, Seattle. He has no conflicts.



The American Cancer Society recommends all U.S. adults at average risk of colorectal cancer (CRC) undergo screening starting at age 45 years.

That update to ACS recommendations is based on an increasing burden of CRC in younger individuals, microsimulation modeling results, and a “reasonable expectation” that screening tests will perform as well in adults aged 45-49 years as they do in older adults, members of the ACS Guideline Development Group said in the guideline, which was published in CA: A Cancer Journal for Clinicians.

Starting screening at age 45 contrasts with recommendations from the U.S. Preventive Services Task Force (USPSTF), which in 2016 gave an “A” recommendation for CRC screening from 50 to 75 years of age. At the time, the USPSTF noted a modest increase in life-years gained by starting earlier, based on microsimulation modeling. But it concluded that available evidence best supported starting at age 50.

The updated ACS guidelines are based in part on a modeling study that the authors say extends the previous analysis conducted for the USPSTF.

“The recommendation places a high value on the potential years of life saved, addresses anticipated rising incidence going forward, and is expected to contribute to the reduction in disparities in incidence before age 50 years in some racial groups,” the ACS guideline authors added.

The recommendation to start screening at age 45 is a “qualified” recommendation, the authors said, given the limitations of the current evidence base. Most studies to date have been focused on older individuals, in keeping with long-standing recommendations to start screening at age 50.

The move downward in screening age recommendation acknowledges one of the most “significant and disturbing” developments in CRC, the guideline’s authors said: the marked increase in incidence among younger individuals.

While CRC incidence and mortality have been declining in adults aged 55 years and older, recent studies cited in the ACS guideline document show a 51% increase in incidence from 1994 to 2014 – and an 11% increase in mortality from 2005 to 2015 – for adults younger than 55 years.

The current age-specific incidence rate for adults 45-49 years is 31.4 per 100,000, compared with 58.4 per 100,000 in adults 50-54 years. However, the ACS guideline authors said the higher rate in the older cohort is partly influenced by more frequent screening. “The true underlying risk in adults aged 45-49 years is likely closer to the risk in adults aged 50-54 years than the most recent age-specific rates would suggest,” they wrote.

Since patients in this age range have not been routinely screened before, the ACS recommendation is based on modeling. Now we need to analyze the outcomes of early screening to identify which patients will benefit most. Choices for screening include either a structural examination or a high-sensitivity stool-based test, according to the guideline, which doesn’t state a preference for any particular test.

The AGA, in their statement in response, noted that with CRC rates rising in people younger than age 50, it is appropriate to consider beginning routine screening at age 45. The statement continues “Since patients in this age range have not been previously routinely screened, the ACS recommendation is based on modeling. Now we need to analyze the outcomes of early screening to identify which patients will benefit most.”


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