The research found that, among adults under 50 who underwent colonoscopy for any reason, those with rectal bleeding had an 850 percent higher risk of being diagnosed with early-onset colorectal cancer compared with people without this symptom.
Rectal Bleeding Linked to Higher Cancer Risk
Presented at the American College of Surgeons Clinical Congress 2025 in early October, the latest study analyzed data from about 450 adults under 50 who had a colonoscopy at the University of Louisville Health System. Researchers collected pathology reports, demographics, symptoms, and family history.
Among this group, about 45 percent were diagnosed with early-onset colorectal cancer, and the other 55 percent had normal results.
About 70 percent of young adults diagnosed with colorectal cancer had no family history of the disease.
Nearly 9 in 10 people diagnosed with cancer got a colonoscopy because they had symptoms. Close to 40 percent of people with cancer presented with rectal bleeding; they were also more likely to be former smokers.
The findings should help doctors decide when to recommend early screening for their patients under 45, the authors wrote.
“We are, unfortunately, diagnosing at an earlier age,” says Himabala Ghanta, MD, a colorectal surgeon at Holy Name in Englewood, New Jersey, who was not involved with the research.
“Even though we don’t want to scare people, we do need to make people aware that if something is not your normal daily routine — if it’s happened maybe more than once or twice or three times — let’s not ignore it, let’s actually talk about it, let’s present the problem to someone who may be able to help you figure out what’s going on.”
What Is Rectal Bleeding?
“It can be the faint red streaks on the toilet paper, or a little bit of blood on top of the stool, or it can be heavier bleeding,” says V. Liana Tsikitis, MD, a professor and division head of gastrointestinal and general surgery at Oregon Health and Science University in Portland. Dr. Tsikitis, who was not involved with the new research, also serves as the Oregon state chair of the American College of Surgeons Commission on Cancer.
- Bright red blood on stool, in the toilet, or on toilet paper after wiping
- Black or tarry stools
- Blood coming from the rectum
It’s important to note that rectal bleeding doesn’t always signal colorectal cancer, though, says Dr. Ghanta.
“Most rectal cancers will present with on-and-off bleeding,” Tsikitis says. “So it’s not necessarily every single bowel movement.”
However, if you’re in your thirties or forties and notice it, “a red flag should be raised,” she says, and you should talk to your primary care doctor.
Pay Attention to Other Symptoms, Too
- Anemia
- Light-headedness
- Chest pain or shortness of breath
- Abdominal, pelvic, or rectal pain
- Fever
- Nausea or vomiting
- Difficulty swallowing
- Unexplained weight loss
Another important one: changes in your bowel habits.
Everyone’s bowel habits are different, Ghanta says. “But if it’s a change for you, it’s something to be a little more concerned about.”
“I don’t want young people to panic,” Tsikitis said. “I just want them to be alerted. I want them to investigate when something doesn’t seem right. It’s okay to be wrong and go and be reassured. If your body’s telling you something is changing, and you cannot explain it in any way, have this discussion with your primary care physician.”
