A new analysis of nearly 200,000 adults shows that those with a clean result on their first colonoscopy may not need another for longer — perhaps significantly longer — than the current recommendation of 10 years.

The result is a bit of good news about a cancer whose increasing rates in younger patients has worried experts, including the Harvard Chan School’s Mingyang Song, for several years. Colorectal cancer is the nation’s second-deadliest after lung cancer, killing an estimated 52,550 in 2023. While rates among older patients have been declining, younger patients — those 40 to 49 — have seen cases rise 15 percent between 2000 and 2026. Experts aren’t sure of the cause, but in 2021, the U.S. Preventive Services Task Force lowered the recommended age of first screening to 45 from 50. They also recommend that those with average risk get screened 10 years afterward.

Song, an associate professor of clinical epidemiology and nutrition at the Chan School, said that the increase in screenings has also increased appointment wait times.

“Especially with the lowered age, the clinic is overwhelmed,” said Song, also an associate professor at Harvard Medical School. “It was overwhelmed before, now it’s even worse.”

In the work, published last month in JAMA Oncology, Song and colleagues examined colorectal cancer screening results and colorectal cancer incidence among 195,453 participants in three long-running studies: the Nurses’ Health Study, Nurses’ Health Study II, and the Health Professionals Followup Study. They compared incidence between two groups: those who received negative results in their initial colorectal cancer screening — meaning no polyps or cancer — and those who had not yet been screened.

They found that the risk of developing colorectal cancer was significantly lower among those who had received a negative cancer screening than those who had not yet been screened. The research team, led by first author Markus Knudsen, a postdoctoral fellow in Song’s lab, then divided the negative screening result group according to lifestyle risk factors for colorectal cancer. The work was supported in part by the National Institutes of Health.

The results showed that it took 16 years for those with a negative screening result and an intermediate-risk lifestyle to have the same colorectal cancer incidence of the unscreened group at 10 years. Those with negative screening and a low-risk lifestyle — including a healthy diet and exercise — didn’t reach the 10-year cancer incidence of the unscreened group until 25 years from their negative screening.

The results, Song said, show that cancer screening should be individualized and discussed between patient and physician. While it is likely that additional evidence will be needed before national screening guidelines are changed, those with a negative screening result may be able to safely extend the screening interval beyond the recommended 10 years and, for those also living a low-risk lifestyle, perhaps as long as 20 years.

What this more tailored approach would do, Song said, is spare those who might get little benefit from a colonoscopy while focusing increasingly scarce resources where they’re most needed: on people who’ve never been screened — only about 70 percent of eligible U.S. adults have been screened — on disadvantaged groups with historically lower screen rates, and on those whose lifestyle or family history puts them at increased risk.  

“What we have seen generally is that the more advantaged groups of individuals are more likely to receive colonoscopy, whereas those who are disadvantaged and who actually have a higher risk of developing colon cancer are less likely to receive colonoscopy,” Song said. “We’ve tried to correct this mismatch and improve colonoscopy delivery at the population scale.”