By Monica J. Smith

 

Adding to the growing body of research that supports initiating screening for colorectal cancer at 45 years of age, a new modeling study suggests that use of stool-based tests in younger people could reduce the incidence of the disease and save lives, even when adherence is less than perfect.

“One concern of starting screening at age 45 is that we’ll divert colonoscopy, which is not an unlimited resource, from patients 50 and older who are at higher risk for colorectal cancer,” said Deborah A. Fisher, MD, MHS, the lead author of the research. “This model shows that screening with the fecal immunochemical test [FIT] or multitarget stool DNA (mt-sDNA; Cologuard, Exact Sciences) improves all outcomes when screening starts at age 45.”

To estimate the effect that screening younger patients would have on outcomes, Dr. Fisher, an associate professor of medicine at Duke University, in Durham, N.C., and her colleagues applied the CRC and Adenoma Incidence and Mortality (CRC-AIM) microsimulation model to 4 million simulated individuals born in 1975 and who were free of CRC at age 40.

They compared outcomes between those screened between 45 and 75 years of age and those screened between ages 50 and 75. They also looked at how the outcomes changed depending on rates of adherence for the stool tests, whether 100% or rates previously reported in clinical practice, 71% for mt-sDNA and 43% for FIT.

CRC-AIM predicted about 24 life-years gained in individuals who started screening at 45 years of age compared with those who started at 50.

The model predicted a reduction in the incidence of CRC of 64% and 61% in the older and younger cohorts, respectively, using reported adherence rates for mt-sDNA testing, and 54% and 50% using FIT.

Reductions in CRC-associated mortality also were greater in the younger screening cohort compared with the older group—72% and 69% with mt-sDNA and 63% and 59% with FIT—according to Dr. Fisher’s group, who presented their findings at the 2020 virtual meeting of the American College of Gastroenterology (abstract P0723).

Aasma Shaukat, MD, the chief of gastroenterology at the Minneapolis VA Health Care System and a professor of medicine at the University of Minnesota, in Minneapolis, said the main finding of improved outcomes with earlier screening sent a positive message.

“We’re seeing an incidence rate in that group similar to what it was in patients 50 and older 20 years ago, so there’s a societal benefit to starting screening in younger patients,” Dr. Shaukat said.

But she found the study’s projection of adherence rates for the stool-based screening methods a bit presumptive: “We don’t know the adherence rate for the younger cohort because we’ve never screened this group before, so that’s a weaker part of the analysis.”

Dr. Fisher acknowledged the study’s limitations. “It is a modeling study, and the validity of the output relies on the validity of the input. So much screening is accomplished by colonoscopy in the U.S. that it is difficult to obtain robust data on the actual adherence to FIT,” she said. “But I think the general principle, that you still have improvements with an earlier initiation age, even when the adherence rates modeled are much lower than 100%, is very supportive and encouraging.”

The findings aren’t immediately applicable to practice, Dr. Shaukat noted. “We would want to get some direct patient data; put a group of 45- to 49-year-olds through screening and see if the results of modeling bear out. We would also want to research the best screening modality.”

Also, payors might not reimburse screening in younger patients, at least not yet, Dr. Fisher added. “If the U.S. Preventive Services Task Force guidelines final draft includes at least a grade B recommendation for starting screening at age 45, this study provides evidence for a path forward that might be less resource-intensive and more feasible.”

The original version of this article indicated that the U.S. Preventive Services Task Force used CRC-AIM to develop guidelines for CRC screening. The USPSTF modeling was completed by Cancer Intervention and Surveillance Modeling Network and included the SimCRC, CRC-SPIN and MISCAN models.

This article is from the July 2021 print issue.