In 2025, a preliminary study presented at the American Society of Clinical Oncology Annual Meeting (ASCO 2025) sparked conversations about extreme running and colon cancer risk. The study’s results are now published in Cancer Epidemiology, reigniting some of the same questions and concerns. The findings show that none of the 92 extreme runners in the study had colon cancer. However, adenomas, precancerous polyps that may transform into cancer over time, were detected in nearly half of the runners and advanced adenomas in 15%.

 

“It’s a super interesting study,” said gastroenterologist Amy S. Oxentenko, MD, a marathon runner who serves as the vice dean of practice at the Mayo Clinic, in an interview with The Washington Post. “But let’s be real. It’s also a very small study, and the findings are quite preliminary, at best. Runners shouldn’t panic. There’s still so much more to learn.”

 

Colorectal cancer is the third most common cancer and the second-leading cause of cancer-related death in the United States. The American Cancer Society estimates that there will be 108,860 new cases of colon cancer and 49,990 new cases of rectal cancer this year. Since 2013, incidence rates of colorectal cancer have dropped by about 1% each year, likely due to increased screening, but rates have increased among people younger than 50 by 2.9% each year.

 

Early detection and treatment of colorectal cancer can increase the likelihood of long-term survival. Colorectal cancer can be detected through a blood test, stool test or colonoscopy, though irregular findings in a blood or stool test should always be followed up by a colonoscopy. Colonoscopies can detect irregular growths on the inner lining of the colon or rectum called polyps. These benign tumors are a primary precursor to colorectal cancer and are typically removed during a colonoscopy. 

 

The United States Preventive Services Task Force recommends all adults should begin regular screening for colorectal cancer at age 45, but those who develop symptoms or are at higher risk should begin screening sooner. Symptoms include changes in bowel habits, blood in the stool, abdominal pain, persistent feeling of needing to have a bowel movement, unexplained weight loss and iron deficiency.

 

To learn more, check out Cancer Health’s Basics: “Colorectal Cancer (Colon Cancer and Rectal Cancer).”

 

For the study involving runners, researchers from the Inova Schar Cancer Institute in Virginia administered surveys to 94 adults who had completed at least two ultramarathons or at least five marathons and did not have a colonoscopy in the last 10 years. The runners, who had an average age of 42, underwent a colonoscopy, and their results were compared to asymptomatic colorectal cancer rates for people ages 40 to 49.

 

Adenomas, a type of precancerous polyp, were detected in 41.5% of participants, and advanced adenomas were detected in 15%, exceeding historical screening benchmarks for the participants’ age group. No colorectal cancers were detected among the runners.

 

So does extreme distance running increase colorectal cancer risk?

 

“We don’t know at this point,” senior study author Timothy L. Cannon told The Washington Post. “But I do think there’s a signal here, and it’s worth paying attention to.”

 

While the study revealed a correlation between extreme distance running and colorectal adenomas, it did not suggest causation. In general, exercise can lower an individual’s risk of several commonly occurring cancers, including bladder, breast, colon, endometrial (innermost lining layer of the uterus), esophagus, kidney, lung and stomach, according to the Centers for Disease Control and Prevention.

 

Cannon went on to emphasize the importance of reporting colorectal cancer symptoms to a doctor, including bloating, cramping and rectal bleeding.

 

“Don’t let anyone tell you that rectal bleeding is normal for runners,” said Cannon. “Get it checked.”

 

To learn more about exercise and cancer, click #running, where you will find stories such as: