A Seismic Shift -- and a Grand 'Experiment' -- in Colorectal Cancer Screening

Mark A. Lewis, MD


November 12, 2020

This transcript has been edited for clarity.

Hello, Medscape. This is Mark Lewis, a gastrointestinal (GI) oncologist at Intermountain Healthcare in Salt Lake City, Utah.

I am recording this video at the end of a rather remarkable week in the field of GI oncology. On October 27, the US Preventive Services Taskforce (USPSTF) released a draft recommendation to begin screening for colorectal cancer at the age of 45 years rather than the age of 50.

I have a couple of comments to share.

First, the USPSTF recommendation now harmonizes with that of the American Cancer Society (ACS), which in May 2018 issued the same recommendation. The gulf between those two organizations on this particular issue has now closed.

With all due respect to the ACS, the USPSTF carries a lot more weight with regard to insurance coverage. They are one of the four agencies that, when they issue and finalize a recommendation like this, insurers are mandated to cover that preventive service. This may be seismic in how patients can access preventive and screening measures for colon cancer in the age demographic of 45-49 years.

The USPSTF has this draft open for public commentary through the end of November before a final recommendation will be issued. As it stands now though, they issued this draft with grade B strength of evidence, which would mandate insurance coverage. That is extremely significant.

Second, I observed various reactions online, with some appropriately rational but some rather emotional and drawing an unfair straight line between this recommendation and the untimely death of Chadwick Boseman.

While I'm the first to admit that early-onset colorectal cancer is an extremely vexing problem, Mr Boseman, to the best of our knowledge, was diagnosed when he was 39 years old and then succumbed to his metastases at age 43. I will point out that the African American population is particularly prone to early-onset colorectal cancer. But, it's not entirely certain that Mr Boseman would have been saved, even with this shift in screening age.

We need to be careful not to conflate screening colonoscopy and diagnostic colonoscopy. One of the greatest tragedies I see in my practice is patients who have had very real symptoms of bleeding in the GI tract, whether that is visible hematochezia or otherwise unexplained anemia, and have not gotten a proper workup. That, of course, is a very different scenario from screening, which is deploying various interventions across the general population. According to some estimates, by shifting the age to 45, you almost immediately add 10-20 million Americans to the eligible screening population. I've seen some concern that this would overwhelm gastroenterology. The USPSTF did not specifically recommend endoscopic intervention; screening can include noninvasive tests of the stool.

Although it may seem counterintuitive, we actually have less evidence as it stands behind full colonoscopy than we do behind flexible sigmoidoscopy. If you look at randomized controlled trials (RCTs) and even some meta-analyses thereof, there is more benefit for flexible sigmoidoscopy. And there seems to be a latency period between when you intervene with flexible sigmoidoscopy and when you see a benefit from colorectal cancer mortality. We're intervening on the adenoma-to-carcinoma sequence in the distal colon when we do flexible sigmoidoscopy. As it happens, that is where the preponderance of young onset colorectal cancers lie. We know that 80% of them occur distal to the splenic flexure.

There is a lot of work still to be done. While I know it's not the same thing as an RCT, once this recommendation is implemented, we will gather a lot of information about which screening methods are used and which ones actually make a meaningful impact. Some critics say that we have put the cart before the horse. We're making this rather sweeping recommendation, largely based on modeling and life-years gained in those models rather than performing a RCT.

I'm particularly interested to see whether flexible sigmoidoscopy continues to show stronger evidence than full colonoscopy, in terms of efficacy and lower complication rate. As a screening method, flexible sigmoidoscopy has a known mortality benefit, which is unlike other screenings, such as mammography and Pap smear (which has been replaced by HPV testing for cervical cancer) that we accept in women's health, for example.

I think this is going to be a very large "experiment" in colorectal cancer. We have to be careful not to incur excessive risk until there is proven benefit. And at this point, I would not discount the potential detection power of the noninvasive test that can prompt endoscopic investigation.

It's a very interesting time — not just for GI oncology but also for primary care and preventive health. This is Mark Lewis for Medscape, signing off.

Mark A. Lewis, MD, is Director of Gastrointestinal Oncology at Intermountain Healthcare in Salt Lake City, UT. He has an interest neuroendocrine tumors, hereditary cancer syndromes, and patient-physician communication.

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