Colorectal Cancer Rates Are Rising Again, and Not Just in Younger Adults

For decades, colorectal cancer was one of the few cancers in the U.S. becoming less common, largely because of screening. A new study suggests that trend may be reversing, and not only in younger adults.

The study, published in NEJM Evidence, found that the overall rate of colorectal cancer in the U.S. rose in 2023 for the first time in more than 20 years. Rates appeared to increase in every age group up to 65 to 69.

Colorectal cancer is the second leading cause of cancer-related deaths in the U.S. and the leading cause among adults younger than 50.

A 20-year decline reverses

Caitlin Murphy, Ph.D., M.P.H., professor of pediatrics and public health sciences at the University of Chicago, and her colleagues analyzed data from the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) Program. The data cover about 46% of the U.S. population.

The age-adjusted rate of colorectal cancer fell from 55.2 cases per 100,000 people in 2000 to 36.7 per 100,000 in 2022. In 2023, it rose to 38.3 per 100,000. The researchers called the increase modest, but it was the first since the data set began in 2000. The pattern was similar for men and women, across racial and ethnic groups, and across cancer stages.

People born in the 1960s and later face higher risk

Murphy said she expected rates to rise in older adults as well as younger ones. The researchers believe the increase reflects what’s known as a birth cohort effect, meaning people born during and after the 1960s face a higher risk of colorectal cancer as they reach middle age and older adulthood.

“I think of a birth cohort effect as the interaction of age and time,” Murphy said. “As people born around the same time move through time and age together, we’re going to see more colorectal cancers being diagnosed.”

Earlier screening explains some, but not all, of the rise

The sharpest increase was among people ages 45 to 49, where rates rose about 12.8% per year from 2019 to 2023. The researchers said this is likely because more people in that age group are getting screened since national guidelines lowered the recommended starting age for screening from 50 to 45. Murphy said this means screening is catching cancer earlier, as intended.

Screening doesn’t explain the increases in older adults, though. Rates rose among people ages 65 to 69 and leveled off among those ages 70 to 74. These groups have historically benefited most from screening, and about 80% are up to date with it. The researchers said unknown risk factors may be offsetting those gains.

The team also checked whether disruptions to screening during the COVID-19 pandemic could explain the trend. The increase persisted even when data from 2020 and 2021 were excluded, and screening had largely returned to pre-pandemic levels by January 2021.

“These results motivate us to understand reasons for this rise, so risk factors can be identified and possibly reduced,” said Sonia Kupfer, M.D., director of the Gastrointestinal Cancer Risk and Prevention Clinic at UChicago Medicine.

Looking for the cause in environmental exposures

The rise in colorectal cancer among people younger than 50 has received widespread attention. According to the American Cancer Society, rates among adults ages 20 to 49 increased 3% per year from 2013 to 2022.

“I think our study shows that we can consider that whatever might be causing colorectal cancer in younger people is now also causing it to increase in older people as well,” Murphy said.

Researchers don’t yet know which risk factors are driving the trend, but Murphy’s team is studying environmental chemical exposures as one possibility. Working with Xin Hu, Ph.D., a toxicologist at Emory University, they plan to measure thousands of environmental exposures in small blood samples to flag chemicals for further study. They will then work with Kupfer to test how those chemicals affect the colon using organoids, lab-grown models of colon tissue.

If the trend continues, Murphy warned that more diagnoses among a large, aging population could put heavy strain on the health care system for cancer treatment and survivorship care.

Screening options from colonoscopy to at-home tests

Until more is known, screening remains the best way to find colorectal cancer early. National guidelines recommend that adults at average risk begin regular screening at 45 and continue through 75. For people younger than 45 or older than 75, screening decisions should be based on family history, symptoms and other health conditions.

Colonoscopy remains the gold standard, but blood-based tests and at-home stool tests are also available.

“There are several ways to do screening that should be discussed with a clinician, so people know what the different screening tests are intended for and how often these need to be repeated,” Kupfer said.

For people younger than 45 who aren’t yet eligible for screening and don’t have genetic risk factors or a family history, Kupfer stressed the importance of watching for symptoms such as blood in the stool, changes in bowel habits or unexplained weight loss, and seeing a doctor if they occur.