Colorectal cancer has long been considered a disease that mostly affects older adults. However, recent research shows that younger adults under the age of 50 are being diagnosed more often.
A new study presented at the American College of Surgeons Clinical Congress 2025 sheds light on one important warning sign that should never be ignored: rectal bleeding.
This study looked at 443 patients under age 50 who had a colonoscopy at the University of Louisville Health System between 2021 and 2023. Out of these patients, 195—about 44%—were found to have early-onset colorectal cancer. The other 248 patients had normal colonoscopy results.
Researchers found that those who had rectal bleeding before the procedure were much more likely to be diagnosed with colorectal cancer. In fact, rectal bleeding made it 8.5 times more likely that a person would have colorectal cancer, compared to someone without that symptom.
This is a major finding because people under 45 are not normally recommended for routine colon cancer screening unless they have a family history of the disease.
But this research suggests that rectal bleeding should be taken seriously in all adults, even those who are young and don’t have a family history of cancer. In many cases, the people who were diagnosed with cancer had no known risk factors.
Dr. Sandra Kavalukas, a colorectal surgeon and one of the study’s authors, said that many of the younger patients she sees with colorectal cancer have no family history.
She explained that this study helps answer an important question: who should get a colonoscopy before the standard screening age? According to her, if a person under 45 has rectal bleeding, doctors should strongly consider doing a colonoscopy.
The study also found that the majority of young adults diagnosed with colorectal cancer—88%—had undergone colonoscopy because they were experiencing symptoms such as bleeding.
On the other hand, only 55% of the people without cancer had symptoms. This means that symptoms, especially bleeding, can be an important clue that something is wrong.
Interestingly, only 13% of the cancer patients had genetic markers commonly linked to hereditary cancer conditions. This means that most of these cancers were not caused by inherited genes.
While having a family history of colon cancer did slightly increase the risk—about two times higher than average—it was still not as strong a risk factor as rectal bleeding.
The study also noticed that former smokers were almost twice as likely to have colorectal cancer compared to people who never smoked. This suggests that lifestyle choices may also play a role in early-onset colorectal cancer.
Dr. Kavalukas gave a clear example to help doctors decide when a colonoscopy is necessary. She said that if a 35-year-old comes in with rectal pain but no bleeding, they probably don’t need a colonoscopy. But if that same person has bleeding, then their risk of cancer is much higher, and a colonoscopy could save their life.
This research is important because more young adults are being diagnosed with colorectal cancer, but they often don’t qualify for screening under current guidelines.
Right now, the U.S. Preventive Services Task Force recommends routine screening starting at age 45 for people without a family history. But these findings suggest that symptoms should be taken into account, no matter a person’s age.
The research team is now working on a larger study. They hope to develop a simple risk calculator that will help doctors decide which young patients need a colonoscopy based on their symptoms and risk factors.
In summary, this study strongly supports the idea that rectal bleeding in younger adults is not something to ignore. Even in the absence of family history or genetic risks, bleeding can be a sign of cancer. Early testing could lead to early diagnosis, better treatment, and potentially save lives.
If you care about cancer, please read studies that a low-carb diet could increase overall cancer risk, and vitamin D supplements could strongly reduce cancer death.
For more information about health, please see recent studies about how drinking milk affects the risks of heart disease and cancer and results showing higher intake of dairy foods linked to higher prostate cancer risk.
Copyright © 2025 Knowridge Science Report. All rights reserved.
