ACS: Start colorectal cancer screening at age 45

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.

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.