Rectal bleeding linked to 850% higher risk of colorectal cancer in adults under 50

A new study from University of Louisville Health has found that rectal bleeding may be the most important warning sign for colorectal cancer in adults under 50—boosting the risk by 850%. The research highlights that nearly 70% of young patients diagnosed had no family history of the disease, raising concerns that current screening guidelines could be overlooking at-risk individuals.



Rectal bleeding as a key predictor



The study, published after reviewing the medical records of 443 patients under 50 who underwent colonoscopies between 2021 and 2023, revealed striking results: almost half of those patients were diagnosed with early-onset colorectal cancer. Among all symptoms reported, rectal bleeding stood out as the most significant predictor.

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"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. "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."



What the study found




The research highlighted several key findings:



Symptom-Driven Care: 88% of patients later diagnosed with early-onset colorectal cancer had undergone colonoscopy because of symptoms like bleeding, compared to just 55% of those without cancer.



Limited Role of Genetics: Only 13% of cancer cases showed genetic alterations linked to hereditary syndromes, and family history increased risk only two-fold.



Lifestyle Risks: Former smokers were found to have almost double the odds of developing early-onset colorectal cancer.



Screening gaps and clinical implications




Currently, US guidelines recommend routine colorectal screening starting at age 45 for average-risk adults. But with cases rising sharply among younger patients, experts caution that symptoms such as rectal bleeding should not be ignored.



"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, according to University of Louisville Health, is intended to help clinicians better identify which younger adults should be prioritized for diagnostic colonoscopies, even if they fall outside traditional screening age groups.