Lowering the age for colon cancer screening: What could go wrong?

The US Preventive Services Task Force (USPSTF) recently issued a draft recommendation to lower the starting age of colorectal cancer screening (CRC) from 50 to 45. For this age group, the USPSTF gave the evidence a “B” grade, meaning that they “concluded with moderate certainty that the net benefit of screening for colorectal cancer in adults ages 45 to 49 years is moderate.” A “B” grade also requires insurers to cover these screenings with no co-pay, under the Affordable Care Act.

Given the potential impact on screening access and utilization, it is important to examine both the potential benefits and harms of this guideline change.

Incidence rising

The impetus for the guideline change is 2017 data showing rising incidence of CRC in people under 50, a 22% relative increase in cases from 2000 to 2013. “Basically a 45-year-old today has the same risk of getting colon cancer as a 50-year-old from years past,” said USPTSF Chair Dr. Alex Krist, professor of family medicine and population health at Virginia Commonwealth University. Considering this change, it makes sense to consider expanding screening.

Yet it is not clear whether the increased incidence is because of a rise in colonoscopies in this age group or because of actual increased disease burden. Another study from 2017 found that utilization of colonoscopies among younger adults increased from 2000 to 2009, which may have contributed to increased CRC incidence.

If we assume that increased CRC incidence in younger adults is due to more disease burden, how would more screening help this age group? The USPSTF used modeling to estimate how many people would benefit from expanding screening. According to their models, performing colonoscopies every ten years for all adults starting at age 45 would avoid 1-2 additional deaths from CRC per 1000 people screened, compared to starting at 50.

Given that millions would be screened, that’s a lot of deaths prevented. However, this scenario would also require hundreds more colonoscopies and lead to 1-3 more complications per 1000 people screened. As a comparison, screening starting at age 50 prevents 24-27 CRC deaths compared to not screening at all, according to their models. Shifting the age of screening from 50 to 45 is a much less dramatic benefit.

It is also important to note that these benefits in the USPSTF recommendation are theoretical, because they are based on modeling projections rather than clinical trials of screening. The models assume that CRC works the same in younger people as it does in older people– that the increased incidence in CRC for young people is because they are at greater risk of adenomas (which can be detected and removed), not that the adenomas are faster to malignancy. Most clinical trials of CRC screening do not include many people under 50, so we don’t know whether CRC can be detected similarly in this age group with screening. Another difficulty is that the model projection is based on 100% adherence to the guideline, which is unlikely to happen in practice.

“It’s essential that someone actually study the diagnostic yield of screening colonoscopy and non-invasive tests in the general population 45-49 year-olds before mandating that insurance cover these tests routinely,” said Dr. Kenneth W. Lin, Associate Professor of Family Medicine at Georgetown University School of Medicine.

Reducing disparities

USPSTF panel members have emphasized that the CRC risk for young Black people is higher than for white people, and that providers should prioritize screening Black people. Their hope is that lowering the screening age will reduce racial disparities in CRC cases and deaths.

Looking at racial disparities in CRC cases and deaths, increasing CRC awareness and access to care for Black people and other people of color is crucial. But is lowering the screening age for everyone the best way to do that? Theoretically, the B grade for screening will make CRC screening covered under insurance, making it more available. However, if young white people rush to get screened, this could reallocate resources in the wrong direction.

“I worry that the limited capacity of colonoscopists – particularly in the COVID-19 era – may mean that rather than increasing uptake of screening in older adults (say, 60-69) where the absolute benefits of screening are much larger, available slots will be filled by health-conscious 45-49 year-olds with a much lower likelihood of benefit,” said Lin.

Other clinicians had this same concern. Lowering the screening age may worsen population outcomes if instead of searching for the 50 year olds who do not get screened, we take the 45 year olds who leap at it, wrote Dr. Vinay Prasad, Associate Professor at UCSF, on Twitter.

As we’ve previously written, media coverage of these guideline changes should better distinguish between screening asymptomatic individuals and diagnostic screening of people with symptoms. Explanations of CRC screening in the media often include stories from younger patients who had symptoms but were not believed by their doctors. We obviously need greater awareness among clinicians about the risk of CRC for younger people, but lowering the screening age for asymptomatic people is not the same thing.