Rectal Bleeding Boosts Colorectal Cancer Risk By 850% In Under-50 Adults, Study Finds

A new study has identified rectal bleeding as the most significant predictor of colorectal cancer in adults under 50, increasing the risk by an alarming 850%. 

The research, conducted at the University of Louisville Health, analyzed medical records of 443 patients under the age of 50 who underwent colonoscopies between 2021 and 2023. Nearly half of those examined were diagnosed with early-onset colorectal cancer. Among all symptoms, rectal bleeding emerged as the clearest warning sign.

"Many of the early-onset colorectal cancers that I see have no family history," said senior author Sandra Kavalukas, MD, FACS, a colorectal surgeon at the University of Louisville School of Medicine in Louisville, Kentucky. "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." 

Key Findings  Of The Study

Symptom-Driven Care: The vast majority (88%) of patients later diagnosed with early-onset colorectal cancer underwent colonoscopy due to symptoms, such as bleeding, compared to just over half (55%) of non-cancer patients.  

Limited Role of Genetics: Only 13% of early-onset colorectal cancer cases had a marker often associated with hereditary syndromes, such as genetic alterations that occur in some colorectal cancers. A family history of colorectal cancer, while a factor, was only associated with a two-fold increase in odds.  

Lifestyle Risk: Patients diagnosed with early-onset colorectal cancer were also significantly more likely to be former smokers (almost two times higher odds). 

Currently, standard guidelines recommend colorectal screening starting at age 45 for those without a family history. However, with rising cases among younger adults, experts warn that many at-risk individuals could be missed. Dr Kavalukas hopes the findings will support more proactive screening decisions, especially for young adults with symptoms like rectal bleeding.

"If they're 35 and they come in with rectal pain, they probably don't need a colonoscopy," Dr. Kavalukas explained. "But if they come in with a bleeding complaint, they are 8.5 times more likely to have a colorectal cancer."

The study aims to help clinicians decide which young, symptomatic patients would benefit from undergoing a diagnostic colonoscopy.