Colon Cancer Signs and Symptoms: What You Need to Know

Medically reviewed by Jeffrey A. Meyerhardt, MD, MPH

Colon cancer is the fourth most common cancer diagnosed in men and women in the United States. Colon and rectal cancers are often collectively referred to as colorectal cancer.

Most colorectal cancers start as a growth on the inner lining of the colon or rectum. These growths — known as polyps — can turn into cancer, but there are also polyps that don’t become cancerous.

Signs of colon cancer

Most patients diagnosed with colorectal cancer do not have symptoms, but there are some signs and symptoms to be aware of, which may include:

  • A change in bowel habits, such as diarrhea or constipation
  • Blood in the stool or dark stools
  • Rectal bleeding
  • Cramping
  • Fatigue
  • Weight loss

These symptoms typically develop when the cancer has progressed, so it’s important to proactively screen for cancer early, before symptoms develop.

Screening is performed via a colonoscopy, which is a physical exam of the colon that may warrant further testing.

How to lower your risk

You can help lower your risk of developing colon cancer by maintaining a healthy weight, getting regular exercise, eating lots of fruits and vegetables, limiting alcohol intake and stopping — or never — smoking. If you notice any change in your bowel habits or are experiencing persistent digestive symptoms, it’s important to contact your doctor.

In the video below, Jeffrey Meyerhardt, MD, MPH, medical oncologist and clinical director of the Gastrointestinal Cancer Center at Dana-Farber, discusses colon cancer risk, what to look out for, and screening guidelines for colon cancer.


Colon and rectal cancer is the fourth most common cancer diagnosed in the United States, and it’s probably also the most preventable cancer.

We know that we can prevent colon cancer and improve mortality through screening.

Those guidelines include checking stool for blood that can’t be seen, includes sigmoidoscopy, or, a full colonoscopy which looks at your entire colon. The most effective screening is a colonoscopy.

Most patients who are diagnosed with colon and rectal cancer don’t have symptoms, but there are certain signs and symptoms that you should alert your primary care physician or other care providers. Those would include bleeding in the stool, abdominal bloating, unexpected weight loss, and if you have blood tests and you’re found to be anemic, those are reasons to screen for colon and rectal cancer.

If you have these symptoms, it does not mean that you have colon or rectal cancer, but it is a reason to alert your physician to be able to look further into your symptoms.

Current guidelines suggest for patients to start screening at age 50, unless they have certain risk factors. Those would include having a family history — particularly, people who’ve had younger family members who were diagnosed with colon cancer — or, having a colon or rectal polyp, or having certain diseases like ulcerative colitis or Crohn’s disease.

The American Cancer Society recently came out with guidelines to suggest that screening should actually start at age 45; the risk is still very low in those under 50, but it is relatively increasing compared to where it was several decades ago.