Rectal bleeding may be one of the strongest warning signs of colon cancer in younger adults.Researchers are urging people in their 30s and 40s to take the often overlooked symptom more seriously.In a new study, they reviewed recent colonoscopy records from more than 400 patients under the age of 50. Those who had rectal bleeding were 8.5 times more likely to be diagnosed with colorectal cancer, according to the results.Other key findings: 70% of those diagnosed had no family history of the disease— and nearly 90% only got a colonoscopy because of symptoms, not routine screening.The senior author says these findings reveal a care gap for younger adults— too young for routine screening yet facing rising colon cancer rates.Her advice to clinicians: “If a person below the screening age comes in with rectal bleeding, you should seriously consider a colonoscopy.”The study also found that lifestyle factors like smoking may raise risk, while genetics played a smaller role than expected.This research was presented at the American College of Surgeons (ACS) Clinical Congress 2025 Author Affiliations: University of Louisville School of Medicine.Sign up for our weekly HealthDay newsletter