Doctors Warn of Top Colon Cancer Symptom to Watch For

Experts say rectal bleeding is the number-one sign that shouldn't be ignored.

Published on Feb. 26, 2026

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Colon cancer can be difficult to detect early on, as symptoms may be mild or attributed to other conditions. However, doctors agree that rectal bleeding or blood in the stool is the number-one symptom that should prompt a call to your healthcare provider. Other common signs include unexplained weight loss, severe abdominal pain, and persistent changes in bowel habits. Early detection is key, as colon cancer is highly treatable when caught early.

Why it matters

Colon cancer is one of the deadliest forms of cancer, but it is also one of the most treatable if detected early. Knowing the top warning signs, like rectal bleeding, can help people seek medical attention sooner and improve their chances of successful treatment.

The details

Colon cancer can develop without obvious symptoms in the early stages, making it hard to diagnose. When symptoms do appear, they are sometimes mistaken for other conditions like hemorrhoids or constipation. Doctors say the number-one sign to watch for is rectal bleeding or blood in the stool, which should never be ignored or attributed to a less serious issue.

  • According to the experts, colon cancer symptoms may start out mild and not warrant a doctor's visit until the disease has progressed.

The players

John Nathanson, M.D.

A gastroenterologist at NewYork-Presbyterian/Columbia University Irving Medical Center.

Pratima Dibba, M.D.

A gastroenterologist with Medical Offices of Manhattan.

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What they’re saying

“Colon cancer can be hard to diagnose because it can develop asymptomatically. When colon cancer does cause symptoms, they can sometimes be wrongly attributed to other processes like hemorrhoids, infection, or constipation.”

— John Nathanson, M.D., Gastroenterologist

“Don't just blame it on hemorrhoids.”

— Pratima Dibba, M.D., Gastroenterologist

What’s next

Along with watching for the warning signs, it's important to follow your healthcare provider's recommendations for regular colon cancer screenings.

The takeaway

Recognizing the top symptom of colon cancer - rectal bleeding - and seeking prompt medical attention can make a significant difference in detecting the disease early when it is most treatable.