8 Warning Signs of Colorectal Cancer

8 warning signs of colorectal cancer

1. A change in bowel habits (think diarrhea, constipation or narrowing of your stool) that lasts for more than a few days.
2. An urge to have a bowel movement that’s not relieved by having one.
3. Rectal bleeding. “Any bleeding you see, even if it’s just one time, should not be ignored,” says Dr. Daniel Labow, a surgical oncologist at the Nuvance Health Praxair Cancer Center in Connecticut.
4. Dark brown or black stool (which can indicate blood).
5. Cramping or belly pain.
6. Weakness and fatigue.
7. Unexplained weight loss. If you have colorectal cancer, your body releases certain hormones into your bloodstream that can lead to weight loss, even if you continue to eat normally, Labow says.
8. Unexplained anemia. “It could be from losing blood from someplace like your rectum,” Labow says.

What is colorectal cancer?

Colorectal cancer starts in either your colon or your rectum, both of which are parts of the large intestine.

Most of these cancers start out as polyps, or growths on the inner lining of your colon or rectum. “Some types of polyps can turn cancerous, but not all polyps become cancer,” says Dr. David Liska, a colorectal surgeon at the Cleveland Clinic.

If cancer develops in a polyp, it can grow into the wall of the colon or rectum. It starts in the inner layers (the mucosa) and then spreads outward through the other layers. Eventually, it can grow into blood or lymph vessels, travel to lymph nodes and finally spread to distant parts of your body.

Colorectal cancer risk factors

The overall risk of developing colorectal cancer is about 1 in 23 for men and 1 in 25 for women, according to the American Cancer Society. A person’s risk can be lower or higher, depending on other factors, including:

Age. The vast majority of cases of colorectal cancer still occur in people age 50 or older. Why it’s also increasing among those under 50 isn’t yet known. “One theory is that it’s due to changes in the microbiome, the bacteria in your gut that keep it healthy,” Kopetz says.

Race. Colorectal cancer incidence is highest in people who are Alaska Native, American Indian or Black, according to the American Cancer Society. The racial and ethnic disparities are similar when it comes to deaths from colorectal cancer.

Sex. Rates are about 33 percent higher in men than in women. Female sex hormones may offer some protection, and women are also less likely to smoke, which is another risk factor. “In general, women tend to take better care of themselves,” Labow points out.

Genetics. Almost 30 percent of colorectal cancer patients have a family history of the disease. If you have a first-degree relative — defined as a parent, sibling or child — with colorectal cancer, you have up to four times the risk of developing it as someone without any family history. About 10 percent of the time, that’s due to a hereditary condition such as Lynch syndrome or familial adenomatous polyposis. If any of these diseases run in your family, you can undergo genetic testing to see if you have the cancer-causing gene mutation.

Inflammatory bowel disease. People with chronic inflammatory bowel diseases, such as Crohn’s disease or ulcerative colitis, have almost double the risk of developing colorectal cancer compared with those without these diseases. Some preliminary evidence suggests that some of the anti-inflammatory drugs used to treat ulcerative colitis may also lower your cancer risk.

Inactivity. People who are the most sedentary have up to a 50 percent increased risk of colon cancer. The good news is that if you become active later in life, you can likely lower that percentage. A recent study also found that regular exercise may help people with colon cancer live longer.

Obesity. Men with obesity have about a 50 percent higher risk of colon cancer and a 25 percent higher risk of rectal cancer compared with those of normal weight. Women with obesity have about a 10 percent increased risk of colon cancer. Abdominal fat seems especially dangerous.

Diet. An eating pattern rich in fiber and calcium and low in alcohol and red meat appears to lower the risk of colorectal cancer, according to a review of studies published in JAMA Network Open.

Type 2 diabetes. People with type 2 diabetes are more likely to develop colorectal cancer than people who don’t have diabetes. According to the American Cancer Society, researchers suspect that high levels of insulin in people with diabetes may have something to do with the increased risk.

Colorectal cancer screening recommendations

The gold standard of colorectal cancer screening is a colonoscopy. During this procedure, a doctor checks your rectum and colon for polyps (masses of tissue) with a flexible tube while you’re sedated.

You should have this done every 10 years starting at the age of 45, or more frequently if you’re at higher risk of colorectal cancer or if you have any suspicious symptoms, Labow says.

Unfortunately, 4 in 10 Americans 45 and older are not up-to-date on colorectal cancer screening, according to a 2025 report from the Centers for Disease Control and Prevention. “These aren’t pleasant tests, especially colonoscopies, which require a lot of prep and taking a day off of work,” Labow explains.

There are other screening options, including at-home stool sample tests: a fecal occult blood test (FOBT), a fecal immunochemical test (FIT) or the stool DNA test (Cologuard). Just be prepared to have a colonoscopy if your test reveals anything suspicious, Labow stresses.

In July 2024, the U.S. Food and Drug Administration approved a blood test to screen for colorectal cancer in adults 45 and older who are at average risk for the disease.

A study published in The New England Journal of Medicine found that the blood test developed by Guardant Health detected 83 percent of colorectal cancer found during colonoscopy screening of people with average colorectal cancer risk, making it a good option for those who choose not to have a colonoscopy or do stool-based testing, study coauthor Dr. William M. Grady, a gastroenterologist at the Fred Hutchinson Cancer Center, told AARP.

Editor’s Note: This story, originally published May 18, 2021, has been updated to reflect new information.