What to know about colon cancer as cases rise in younger adults

It took three years, four emergency-room visits and multiple misdiagnoses before Reuben Cheatem was diagnosed with stage III colorectal cancer. The painter was living in Mexico just before the pandemic when he developed a severe case of food poisoning that left him in constant pain and experiencing rectal bleeding. Antibiotics and painkillers brought temporary relief, but the symptoms kept returning over the following years.

By the time he was correctly diagnosed in 2022, at age 42, the news came as a shock. He had avoided doing many things, he said, because he thought they caused cancer. For the first 20 years of his artistic career, for example, he steered clear of oil paints, concerned about the solvents and fumes and their potential link to cancer.

Now 46 and in remission, the Dallas-based artist is among a growing number of younger adults diagnosed with early-onset colorectal cancer, now the leading cause of cancer death in the United States for people under 50, according to a new analysis from the American Cancer Society. Early-onset colorectal cancer has been rising for three decades, increasing by about 0.5% to 2.4% each year. Since 2020, these cases have accounted for about 12% of all colorectal cancer diagnoses in the U.S. With March marking National Colorectal Cancer Awareness Month, here’s what to know about colorectal cancer, including warning signs, risk factors, screening options and when to seek care.

What causes early-onset colon cancer? Colorectal cancer begins in the large intestine — which includes the colon and the rectum — when cells grow and divide uncontrollably. The colon makes up the first several feet of the large intestine, while the remaining portion forms the rectum.

Depending on where the cancer starts, it may be referred to as colon or rectal cancer; colorectal cancer is an umbrella term that includes both. No single cause has been identified for the rise in early-onset colorectal cancer, but it is likely driven by an increase in known risk factors, said Dr. Michelle Olson, a colorectal surgeon at Methodist Dallas Medical Center.

“There’s a lot of thought that it has to do with some modifiable risk factors,” Olson said.

“So the obesity epidemic, people being more sedentary and not necessarily following good, high fiber diets.” Over time, these factors can fuel chronic inflammation — the body’s response to injury or infection — creating conditions in the colon that may promote tumor growth and leave lasting changes in the tissue. A recent study from UT Southwestern Medical Center and the University of Texas at Dallas found tumors in young patients diagnosed with colon cancer tended to arise in more scarred, stiffened tissue, with nearby normal tissue showing early signs of these changes, suggesting the colon may be primed for cancer long before it appears.

Another contributor to that inflammation may be that the gut microbiome — the collection of bacteria and other microorganisms living in the digestive tract — is altered by diet or prolonged antibiotic use, said Dr. Nilesh Verma, an oncologist specializing in colorectal cancer at UT Southwestern, who was not associated with the recent study.

“One thing we’ve learned through tissue analysis is that young-onset colorectal cancer patients harbor certain bacteria, like E. coli, that produce toxins,” Verma said.

“What those toxins are doing is breaking down the DNA and promoting inflammation, leading to this carcinogenic state and causing colon cancer.” Certain family histories may increase risk, Olson and Verma said. These include colorectal cancer and Lynch syndrome, a genetic condition linked to several cancers, particularly early-onset colorectal cancer.

A medical history of inflammatory bowel diseases, such as ulcerative colitis or Crohn’s disease, can also raise risk. A recent study from Cornell University found these conditions may draw certain white blood cells to the colon, where they encourage an inflammatory environment that promotes tumor growth. Signs, screening and diagnosis of colon cancer As Cheatem experienced before his cancer diagnosis, one of the most common warning signs is rectal bleeding or blood in the stool.

Other symptoms can include changes in bowel habits or persistent abdominal discomfort, such as pain, bloating or cramping.

“Even things like unexpected appetite changes, weight loss, fatigue in somebody who was previously active and is now tired all the time,” Olson said.

“Those are the types of symptoms that certainly warrant a discussion with your primary care doctor.” The gold standard for screening and diagnosing colorectal cancer is a colonoscopy, a procedure recommended to people age 45 and older in which a camera is used — typically under sedation — to examine the full length of the colon. Any abnormalities, such as areas of inflammation or suspicious growths, can be biopsied and tested.

“You can get an answer right there without another test,” Olson said. Although many doctors recommend colonoscopies as the main screening method, some people may choose to do at-home screening tests that look for colorectal cancer DNA in a stool sample, particularly if they have no symptoms or relevant family history.

“The stool-based tests are really only recommended for people who are considered average risk,” Olson said.

“The minute you have symptoms, that changes what your profile is.” If a colonoscopy back positive for colon cancer, surgery is typically done to remove the tumors or portions of the colon, followed by chemotherapy or other cancer treatment, depending on how advanced the cancer is, Olson and Verma said. How can colon cancer be prevented?

There’s no guaranteed way to prevent colorectal cancer, but Olson and Verma said people can lower their risk by making healthful diet and lifestyle choices.

“It’s really more about modifying those things you have control over,” she said.

“If you’re smoking, quit smoking. If you’re vaping, quit vaping. If you’re sedentary, even doing 30 minutes of walking every day is better than not doing that.”

When it comes to diet, consuming fiber can help lower the risk of colorectal cancer by promoting gut health, supporting healthy bacteria and reducing the time harmful substances stay in the digestive tract. Many Americans fall short of eating enough fiber, with the 2020–25 Dietary Guidelines for Americans indicating low fiber intake as a public health concern. Adult women under under the age of 50 should aim for 25 grams of fiber a day, while men in the same age range should aim for 38 grams a day.

A cup of cooked lentils, for example, has almost 16 grams of fiber, and a cup of canned black beans contains nearly 20 grams of fiber. Verma also recommends limiting consumption of processed and red meats, including beef, pork, veal, lamb and venison. A 2024 study from the University of Southern California’s Keck School of Medicine analyzed data from nearly 30,000 people with colorectal cancer and about 40,000 without it, finding that higher intake of red and processed meat was associated with increased risk of roughly 30% and 40%, respectively.

Compounds formed when meat is cooked at high temperatures are believed to play a role by triggering cancer-causing changes in the colon, according to the Colorectal Cancer Alliance. Some over-the-counter supplements may help reduce the risk of early-onset colorectal cancer, Verma said.