A recent study found that rectal bleeding in adults younger than 50 raises the odds of an early-onset colorectal cancer diagnosis by about 8.5 times, signaling the symptom should be taken seriously rather than dismissed.
Study details: Researchers reviewed 443 patients under age 50 who underwent colonoscopy at the University of Louisville Health System between 2021 and 2023. Of those patients, 195 were diagnosed with early-onset colorectal cancer and 248 had normal colonoscopy results. Most of the young patients with cancer—88%—had colonoscopy because of symptoms rather than routine screening, and 70% had no family history of colorectal cancer. The analysis also found that people who had smoked in the past were more than twice as likely to have early-onset disease compared with never-smokers. The findings were presented at the American College of Surgeons Clinical Congress 2025 in Chicago and have not yet appeared in a peer-reviewed journal.
Clinical implications: Authors and outside experts say both patients and clinicians should treat rectal bleeding in younger adults as a warning sign and consider prompt evaluation, including colonoscopy. Lead study authors at the University of Louisville stress that many early-onset cases occur without a family history, so symptoms, not just family risk, should guide decisions about testing. Other cancer specialists echo that clinicians should not assume bleeding in younger patients is caused by benign conditions like hemorrhoids, and persistent bleeding merits investigation.
U.S. burden and trends: The American Cancer Society estimates there will be more than 150,000 new colorectal cancer cases in the United States this year—over 100,000 colon cancers and just under 50,000 rectal cancers—split roughly equally between men and women. Colorectal cancer remains a leading cause of cancer deaths in the U.S., with about 53,000 deaths expected this year. Although overall incidence has declined since the mid-1980s due largely to screening and lifestyle changes, the trend is different in younger adults: between 2012 and 2021, colorectal cancer incidence rose by more than 2% per year in people under 50, and mortality in this group has inched upward. The National Cancer Institute reports colon cancer is the leading cause of cancer-related death for U.S. adults aged 20 to 49; researchers have noted that people born around 1990 face roughly double the risk of colorectal cancer compared with those born around 1950.
Possible causes and prevention: The reasons for the rise in early-onset colorectal cancer are not yet clear. Suspected contributors include diet, low physical activity, obesity, overuse of antibiotics, chronic inflammation, and shifts in the gut microbiome. Some experts have suggested that exposure to certain gut bacteria in childhood could influence cancer risk decades later.
Screening and symptoms: Early detection greatly improves cure rates, which is why screening matters. Current guidance recommends starting routine screening at age 45 for average-risk adults, with earlier testing for people who have a family history of colorectal cancer or conditions such as inflammatory bowel disease. Colonoscopy is considered the most comprehensive screening option and is typically repeated every 10 years when no polyps are found in an average-risk person; at-home stool-based tests are alternative options. Beyond rectal bleeding, warning signs include changes in bowel habits, persistent diarrhea or constipation, abdominal cramping or pain, and unexplained weight loss. Anyone with a family history of colorectal cancer—especially when relatives were diagnosed at a young age—should discuss earlier screening with their clinician.
Risk-reduction strategies: Practical steps to lower colorectal cancer risk include adopting a high-fiber, lower-fat diet with fewer red and processed meats and more poultry, fish, legumes, fruits, vegetables, and whole grains; getting regular physical activity (about 2.5 hours of moderate activity per week is recommended by several organizations); limiting alcohol; avoiding tobacco; and maintaining a healthy weight. Experts emphasize establishing healthy habits early in life to reduce long-term risk.
Bottom line: Rectal bleeding in people under 50 is not normal and warrants evaluation. Patients who experience this symptom should talk to their doctor about timely diagnostic testing, and clinicians should consider colonoscopy rather than assuming benign causes.
