COMMENTARY

Yet Another New Cancer Screening Recommendation. This Time Up: Colon

Kenneth W. Lin, MD, MPH

Disclosures

July 11, 2018

Editorial Collaboration

Medscape &

Hello, everyone. I'm Dr Kenny Lin, a family physician at Georgetown University Medical Center in Washington, DC, and I blog at Common Sense Family Doctor.

If I didn't know any better, I might think that the American Cancer Society (ACS) is fixated on the number 45. A few years ago, they broke with conventional wisdom and raised their recommended age for most women to begin screening for breast cancer from 40 to 45 years.[1] More recently, they lowered the age for average-risk adults to begin screening for colorectal cancer from 50 to 45 years.[2] Although I agreed with the ACS's decision on breast cancer, I disagree with routinely screening younger adults for colorectal cancer—a decision that I believe is premature at best, and at worst will cause more harm than good. But before explaining why, I will review the thinking behind the ACS's new position on colorectal cancer screening.

Last year, a study by ACS-affiliated researchers[3] found a troubling 22% rise in the incidence of, and a 13% rise in mortality from, colorectal cancer in adults younger than 50 from 2000 to 2013, with the largest absolute increases occurring in adults aged 40-49. It isn't known why this is happening, or how much truly represents an increasing disease burden, rather than earlier diagnoses owing to more colonoscopies being performed for gastrointestinal symptoms in younger adults.[4]

A microsimulation modeling study commissioned by the US Preventive Services Task Force[5] for its 2016 colorectal cancer screening recommendations suggested that a strategy of starting screening earlier than age 50 might be more effective. The ACS asked the authors to update their study using newer incidence data, and their new analysis[6] concluded that starting screening at age 45 rather than age 50 could prevent two deaths from colorectal cancer for every 800 additional colonoscopies performed.

However, there's an important caveat: Few clinical trials of colorectal cancer screening methods included adults younger than age 50, so we don't have real-life data to back up these models' projections of benefit. The rationale for starting screening at an earlier age than in the past is that the incidence of colorectal cancer is higher now, so there are more cancers to be found by screening. But this would only translate into benefits for patients if these cancers behave the same as asymptomatic cancers found in older adults, which is an untested proposition. This is why the American Academy of Family Physicians still recommends starting screening at age 50,[7] using one of three evidence-based methods: fecal immunochemical tests, flexible sigmoidoscopy, or colonoscopy.[8]

What are the harms associated with starting screening 5 years earlier? Any screening method will lead to more colonoscopies, either as a primary screening test or as a follow-up test for an abnormal result. A systematic review and meta-analysis of postcolonoscopy complications[9] found that 1 in 1000 colonoscopies cause bleeding, 1 in 2000 result in perforation, and 1 in 33,000 lead to death. Although complications are rare, they add up quickly when screening millions of eligible adults.

In my mind, more studies are needed to establish the benefits of the ACS's recommendation for earlier screening to be sure than they outweigh these harms.

This has been Dr Kenny Lin for Medscape Family Medicine. Thank you for listening.

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