8 Warning Signs of Colorectal Cancer

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 David Liska, M.D., a colorectal surgeon at Cleveland Clinic.

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

Risk factors to know

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 runs 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 when you’re older, you can likely lower that percentage.

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 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.

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 the American Cancer Society’s 2023 report. “These aren’t pleasant tests, especially colonoscopies, which require a lot of prep and taking a day off of work,” Labow explains. [See: "10 Ways to Have a Better Colonoscopy"]

Another screening option is one of the three at-home stool sample tests: a fecal occult blood test (FOBT), a fecal immunochemical test (FIT) or the stool DNA test (Cologuard).

If you do these regularly (either once a year, or, in the case of Cologuard, every three years), research shows they’re just as effective as a colonoscopy at reducing death rates from colorectal cancer. Just be prepared to have a colonoscopy if your test reveals anything suspicious, Labow stresses.

In July of 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 recently 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 William M. Grady, M.D., a gastroenterologist at the Fred Hutchinson Cancer Center, told AARP.

The screening test was available for doctors to order prior to the FDA’s decision. Its approval, however, likely makes it more affordable and accessible.

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