Colorectal Cancer Screening

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Given that OB/GYNs have one foot in the world of primary care and another foot in the world of specialty care, we thought we’d review these recently updated USPSTF guidelines (5.2021) which have been endorsed by ACOG.

Why do we care?

  • Colorectal cancer (CRC) is the third leading cause of cancer death in the USA for men and women

    • Almost 53,000 deaths from CRC in the US in 2021

  • Most frequently diagnosed among folks aged 65-74, but

    • 10% of cases occur in persons under age 50.

    • 15% increase of incidence in persons aged 40-49 between 200-2016.

  • 26% of eligible adults have never been screened, and 31% are not up to date with screening as of 2018!

What population are we talking about, and who is at most risk?

  • The USPSTF recommendations are limited to “average risk” population, so:

    • Not talking about those with:

      • Genetic syndromes (i.e., Lynch, familial adenomatous polyposis)

      • Inflammatory bowel diseases

      • Personal history of CRC or adenomatous polyps

  • Age is one of the most important risk factors.

    • CRC screening particularly in average risk adults aged 50-75 has significant benefit, and in adults over age 45 also likely has at least moderate net benefit.

      • After age 75, the benefit of CRC screening is lessened, but may still be there for folks who have never been screened.

    • All adults aged 45 or older should be offered screening!

  • Rates of CRC are higher in Black adults, as well as Native adults.

    • This likely reflects complex issues in health disparities and access to screening (which was previously procedural and only colonoscopy or flex-sig based).

      • The USPSTF mentions that this health disparity is not rooted in genetic difference – we appreciate that recognition that race does not equal genetics, and some evidence to back it up.

  • Additional risk factors include:

    • Family history of CRC (even in absence of genetic syndromes)

    • Obesity

    • Diabetes

    • Smoking

    • “Unhealthy” alcohol use

What tests are available for screening, and how do they work?

  • Stool-based tests include high sensitivity guaiac fecal occult blood test (gFOBT), fecal immunichemical tests (FIT), and stool DNA tests. 

    • gFOBT and FIT detect blood in the stool. gFOBT is chemical while FIT uses antibodies.

    • There is one stool DNA test on the market that also includes a FIT component.

    • If one of these tests are employed for screening, it is recommended that:

      • gFOBT or FIT annually

      • sDNA-FIT every 1-3 years

        • FIT and sDNA-FIT annually provides greater benefit than every 3 year schedule, but sDNA annually leads to more colonoscopies; thus, the range is provided to help balance.

        • gFOBT likely has lower sensitivity to detect CRC and advanced adenomas.

          • Positive results on any test should be followed up with colonoscopy.

    • Stool-based tests are quick and non-invasive and don’t require a bowel prep, so likely make screening more available for patients.

      • gFOBT does require some dietary and medication restriction, but FIT and sDNA-FIT do not.

      • gFOBT requires 3 separate bowel movement samples; FIT and sDNA-FIT can be performed from one sample.

        • sDNA-FIT requires collection of an entire bowel movement, though!

    • The benefits of stool-based testing accrue with frequent, repeated testing – so to get max benefit, the annual frequency is definitely recommended!

  • Direct visualization tests look inside the colon and rectum - options are colonoscopy, CT colonography, and flexible sigmoidoscopy. 

    • Flexible sigmoidoscopy uses a scope to visualize the rectum, sigmoid, and descending colon.

    • CT colonography uses x-ray images to visualize the colon.

    • Colonoscopy uses a scope to visualize the entirety of the colon.

      • Flex sig and CT colonography require colonoscopy as a reflex test if an abnormality is found.

    • If one of these tests are employed, recommended screening intervals are:

      • Flexible sigmoidoscopy:

        • Every 5 years alone, or 

        • Every 10 years in combination with annual FIT

      • CT colonography every 5 years

      • Colonoscopy screening every 10 years

        • Colonoscopy and CT colonography provide greater estimated life-years gained versus flexible sigmoidoscopy every 5 years.

    • These are the gold standard in screening, but must be performed in a clinical setting, require bowel preparation, and may require sedation or anesthesia.

Which test should I order?

  • As of the time of the USPSTF recommendation, there were no high-quality trials comparing effectiveness of different strategies to reduce CRC mortality

  • There are also relatively few studies in younger populations (i.e., younger than age 50). 

  • So it’s up to you and your patient’s values/context to decide what will get screening done reliably to reduce their risk!