Colorectal Cancer Rates Rise Across Age Groups Under 70

Colorectal cancer rates are rising across more age groups than earlier trends suggested. A U.S. analysis found that the overall rate increased in 2023 for the first time in two decades, with increases among adults under 70. The findings broaden concern beyond younger adults, though they don’t explain what’s driving the change.

Published in NEJM Evidence, the report analyzed data from the National Cancer Institute’s Surveillance, Epidemiology, and End Results program for 2000 through 2023. It counted 38.3 cases per 100,000 people in 2023, compared with 36.7 per 100,000 in 2022.

The sharpest increase was among people ages 45 to 49: Their rate rose about 13% per year from 2019 to 2023. Rates also increased among adults ages 65 to 69, while they held steady among those 70 to 74. That pattern stands out because rates in the older groups had historically declined.

Lead author Caitlin Murphy, M.D., M.P.H., a professor of public health sciences at the University of Chicago, said the findings mean rising rates can no longer be viewed as a problem limited to younger adults. The study’s authors called for further monitoring and investigation. Their analysis describes changes in recorded cases; it doesn’t identify a cause or show that any single factor explains the rise.

Why rates may be changing

One possible explanation is a “birth cohort” effect: People born in certain decades may face different risks as they age than earlier generations did at the same ages. Murphy said people born during and after the 1960s appear to have higher colorectal cancer risk as they enter middle and older adulthood. Age itself is also a risk factor, so the combination of an elevated risk in these generations and their growing age could help explain rising rates among people in their 50s and 60s.

Screening may help account for the increase among 45- to 49-year-olds. National recommendations lowered the starting age for average-risk screening from 50 to 45, and more screening can lead to more cancers being detected. That explanation doesn’t resolve the increases among people ages 65 to 69, or the plateau among those 70 to 74. The researchers said screening gains may be counterbalanced by risk factors that haven’t yet been identified.

More diagnoses after screening was delayed or missed during the pandemic could also contribute. But the researchers said a catch-up alone seems unlikely to explain the 2023 pattern. The increase remained in their analyses when data from 2020 and 2021 were excluded.

Doctors have also raised possible lifestyle and health factors. These include limited physical activity, excess weight at younger ages, and diets higher in processed meat. Alcohol use, lower fiber intake, and changes in the gut microbiome have also been suggested. These are possible contributors, not confirmed explanations for the recent increase.

Tiago Biachi, M.D., Ph.D., a colorectal cancer specialist at Moffitt Cancer Center, said some diagnoses may reflect pandemic-related delays, while part of the increase is likely real. Generations with higher rates at younger ages may carry that added risk as they grow older. Even so, the reasons remain uncertain, and many people diagnosed with colorectal cancer have no obvious risk factors.

Risk reduction and screening

General habits may help reduce risk. Ketan Thanki, M.D., a colorectal surgeon at MemorialCare Todd Cancer Institute, recommends a diet with fiber from foods such as whole grains and vegetables, alongside limiting red and processed meats. Regular physical activity, avoiding heavy alcohol use, and managing conditions such as obesity and diabetes may also be helpful. These steps can support health, but they can’t guarantee that someone won’t develop colorectal cancer.

Screening remains a central way to find colorectal cancer and precancerous growths. For average-risk adults, screening is recommended starting at 45. Colonoscopy can detect and remove some precancerous growths during the same procedure. Stool-based tests offer a noninvasive option and can work well when repeated as recommended, though they may be less effective at finding precancerous growths.

There isn’t one screening approach that suits everyone. Murphy emphasized that the priority is completing an appropriate test, and Biachi said the most useful option is one a person follows through with. A doctor or pharmacist can help discuss screening choices, timing, and personal risk factors; people with a family history or other concerns may need an individualized discussion with a clinician.

Symptoms deserve attention even before someone reaches the routine screening age. Murphy cited rectal bleeding, ongoing changes in bowel habits, unexplained weight loss, and abdominal pain. These signs don’t necessarily indicate cancer, but they warrant medical evaluation, including in younger adults. The key message from the new analysis is to take changing rates seriously while recognizing that researchers still need to learn why they’re rising.