The last few decades have seen a dramatic rise in early-onset colorectal cancer, or cases that occur in adults under 50. A new study suggests that one symptom in particular may be the strongest predictor of colorectal cancer in this age group: rectal bleeding.
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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.
Researchers said that the findings underscore the importance of taking rectal bleeding seriously, even if you don’t have a family history of colorectal cancer or you’re under age 45, the recommended age to start colorectal cancer screening.
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“This research lends support to the question of who does or doesn’t warrant a colonoscopy. If you have a person below the screening age with rectal bleeding, you should seriously consider a colonoscopy,” the study’s senior author Sandra Kavalukas, MD, a colorectal surgeon at the University of Louisville School of Medicine in Kentucky, said in a statement.
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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?
Rectal bleeding refers to blood that passes from the rectum or anus. It can present in a few different ways.
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“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.
Signs of rectal bleeding can include:
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- 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.
Rectal bleeding could also be a sign of other conditions, such as:
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“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.
The only way to know for sure what’s causing rectal bleeding is to do a rectal exam and a colonoscopy.
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Pay Attention to Other Symptoms, Too
While the study highlights the connection between rectal bleeding and colorectal cancer, it’s not the only symptom to take note of. Here are some other signs to watch for along with bleeding:
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- 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.”
Age doesn’t matter, she adds. If you notice any of these signs, see your doctor, who will recommend the best course of action. And, get a colonoscopy as soon as you turn 45.
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“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.”
