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8 Warning Signs of Colorectal Cancer

​Plus, what you need to know about screening recommendations and risk factors 

spinner image Colonoscopy appointment marked on the calendar during March, which is Colon Cancer Awareness month represented by the blue ribbon
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Health experts are tracking a concerning trend in colorectal cancer: Its burden is shifting to a younger population.

According to a 2024 report from the American Cancer Society, colorectal cancer is now the leading cause of cancer deaths in men under 50 and the second in women of the same age group. Two decades ago, it was the fourth leading cause of cancer deaths in these groups.

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“The continuous sharp increase in colorectal cancer in younger Americans is alarming,” Ahmedin Jemal, senior vice president of surveillance and health equity science at the American Cancer Society, said in a statement. “We need to halt and reverse this trend by increasing uptake of screening, including awareness of non-invasive stool tests with follow-up care, in people 45-49 years.”

The U.S. Preventive Services Task Force updated its guidelines in 2021 to say that individuals should get an initial screening for colorectal cancer at age 45, instead of waiting until they’re 50.

One reason screening is so important is because colorectal cancer, which is expected to affect 152,810 people in the U.S. in 2024, often doesn’t cause symptoms in the early stages, says Scott Kopetz, M.D., a professor in the Department of Gastrointestinal Medical Oncology, Division of Cancer Medicine, at the University of Texas MD Anderson Cancer Center in Houston. And catching the cancer in its earlier stages can be lifesaving.

“One take-home message is that screening shouldn’t be based on symptoms,” Kopetz stresses. “When you do have symptoms, colorectal cancer tends to be more advanced. That’s why it’s so important to follow screening guidelines.”

That said, the following red flags indicate you should be checked out immediately, even if you’ve recently had cancer screening such as a colonoscopy.

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 Daniel Labow, M.D., executive vice chair of the Department of Surgery at the Mount Sinai Health System in New York City.
  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 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.


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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.

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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 at reducing death rates from colorectal cancer as a colonoscopy. Just be prepared to have a colonoscopy if your test reveals anything suspicious, Labow stresses.

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

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