Everyone loves guidelines. Most guidelines summarize evidence to make specific, actionable recommendations that provide a sense of security for young (and not-so-young) clinicians as they navigate busy workdays, imposter syndrome, and fear of malpractice allegations. But just as there is a hierarchy of evidence, validity of guidelines varies based on the quality of evidence available and the transparency with which the development group presents their recommendations. The United States Preventive Services Task Force (USPSTF) represents the best of the best, providing standardized, evidence-linked, and graded guideline recommendations systematically crafted by a mixed group of experts without financial, philosophical, or intellectual conflicts of interest.

You may have heard by now that the USPSTF updated their Grade A recommendation to screen adults aged 50-74 for colorectal cancer to include a Grade B recommendation to screen those aged 45-49 as well. This Grade B screening recommendation reflects moderate certainty that additionally screening those aged 45-49 will result in a moderate net benefit. This update, published only five years after the last guideline in 2016, was prompted in part by cohort trends suggesting a consistent rise in colorectal cancer incidence among adults aged 40-54 (from 0.5% in the mid-1990s to 1.3% in 2013) despite declining overall colorectal cancer incidence. In order to update their colorectal cancer screening recommendations, the USPSTF commissioned a systematic review to assess effectiveness (and comparative effectiveness) of screening tests, test accuracy, and harms of screening, including the number of complications and lifetime tests if screening started at age 45 vs. age 50.

Advice to screen for colorectal cancer is not controversial. It’s the Grade B recommendation to begin screening sooner that leads us to wonder (and many patients to ask), what magnitude of benefit might we expect to see from initiating colorectal cancer screening five years earlier? According to data from the USPSTF-commissioned systematic review, the absolute risk reduction is estimated to be 27 life years gained per 1,000 people screened with colonoscopy and 26 life years/1,000 people screened with stool-based testing. However, both methods only avert one death per 1,000 people screened with the earlier start. The marginal mortality benefit must be weighed against the potential for up to 311 additional lifetime colonoscopies and 3,501 other tests per 1,000 people who start screening at 45 with stool-based testing, and the potential for an additional 784 lifetime colonoscopies per 1,000 people initially screened with colonoscopy starting at 45. Of note, the evidence for colonoscopy-based screening is overall more robust and higher quality than that for stool-based testing, which relies more heavily on modeling studies.

The bottom line is that while guidelines are developed for a population, they must be applied to individuals. Our job is to consider guideline recommendations in the context of the patient in front of us, weighing both the strength of the recommendation and the quality of the evidence supporting it. This requires that clinicians know how to assess the validity of guidelines and actually put in the work to do so (at least once per professional organization, anyway). So, will we continue to recommend colorectal cancer screening for all (average-risk) patients aged 50-74? Definitely. Will we recommend it for all 45-year-olds? Maybe. Probably. What’s clear is that colorectal cancer screening for average-risk 45-year-olds should involve a conversation including the all-but-guaranteed risk of additional lifetime testing, the risk of complications from additional testing, and the small all-cause mortality benefit and modest effect on life years saved with earlier screening.

For more information, see the topic Colonoscopy for Colorectal Cancer Screening in DynaMed.