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Colorectal cancer: 4 warning signs to watch for

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July 3, 2023—Colorectal cancer rates have been rising among young adults since the 1990s. The trend prompted medical groups to lower the age to begin lifesaving screening tests from 50 to 45. But what about even younger adults, for whom screening typically isn't recommended?

Although it is relatively rare, many colorectal cancers are diagnosed in people under 45. Now, researchers have pinpointed four colorectal cancer early warning signs that could help improve early detection rates among those too young to be screened. When colorectal cancer is found at an early stage, the five-year survival rate is 90%, the American Cancer Society (ACS) reports.

Potential red flags

For the study, published in the Journal of the National Cancer Institute, researchers looked at data on more than 5,000 people who were diagnosed with colorectal cancer before age 50. They also looked at data on a control group of 22,000 people who did not have colorectal cancer.

Their findings: Younger adults who had colorectal cancer were more likely than their peers in the control group to experience these four warning signs in the three months to two years before their diagnosis:

Abdominal pain. This was the most common sign linked with an increased risk of early-onset colorectal cancer.

Anemia. This condition (when the blood lacks enough red blood cells to carry oxygen to the body) can be caused by bleeding from a tumor.

Diarrhea. Colorectal cancer can cause this and other ongoing changes in bowel habits, such as constipation or thin stools.

Rectal bleeding. This sign (followed by anemia) had the strongest link to colorectal cancer. Bleeding from the rectum typically shows up as bright red blood.

People who had more of these red flags were more likely to be diagnosed with colorectal cancer. Compared to people who didn't experience the four warning signs, the likelihood of being diagnosed with colorectal cancer was:

  • Nearly twice as high among people with just one of the signs.
  • Six times higher among people who had three or more signs.

Take symptoms seriously

The study's authors say that people who have these potential warning signs should see a doctor without delay.

Other things besides colorectal cancer can cause these signs and symptoms. For instance, hemorrhoids can cause rectal bleeding, and many people get diarrhea now and then. But it's a good idea to see a doctor to be sure—especially if your symptoms last more than a few days, if you have more than one of them or if they go away and return.

You should also know other signs and symptoms of colorectal cancer. According to the ACS, they include:

  • A feeling like you need to have a bowel movement that's not relieved by having one.
  • Blood in the stool, which can make the stool look dark brown or black.
  • Feeling weak and very tired.
  • Losing weight without trying.

Get screened on time

Screening is still the best way to find colorectal cancer early, when it's often easier to treat. And it helps doctors find and remove polyps (growths) that could become cancer. People at average risk should begin colorectal cancer screenings at age 45. If you're at higher risk, your doctor may recommend starting screenings sooner.

When it comes to colorectal cancer screening tests, there are a range of options, each with pros and cons. Your doctor can help you decide which test is right for you.


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