A chart shows the most common symptoms of colon cancer in people under 50, as cases in younger people rise

• The most common symptom of colon cancer in younger adults is rectal bleeding, a study found.

• Rates of colon cancer in people under 55 have risen since the mid-1990s.

• Researchers identified 17 symptoms that patients and doctors should look out for.

Rectal bleeding, abdominal pain, and changes in bowel habits were identified as the most common symptoms of colon cancer in younger adults in a new study.

The disease is affecting more and more younger adults, as rates of colon cancer in people under 55 have risen since the mid-1990s. Research from the American Cancer Society found that from 2011 to 2019, rates increased by 1.9% a year in people younger than 55. Though cases rose in all age groups under 50 during this period, the biggest uptick was seen in people in their late 20s to early 30s. The rate of colon cancer for people in that age group increased by about 70% from 1999 to 2020, according to Centers for Disease Control and Prevention data.

Colon-cancer deaths in younger patients are still rare, however. A 2023 study estimated that patients under 55 accounted for 138,652 out of 1,166,158 total US colon-cancer deaths from 1999 to 2020.

But colon-cancer symptoms, such as weight loss and appetite changes, can be indicative of many illnesses, the authors of the new study published Friday in JAMA Network Open noted. This means the cause is often missed, leading to late-stage diagnoses that are harder to treat.

To combat this, a group of researchers used data from 81 studies across six countries involving nearly 25 million people under 50 with early-onset colon cancer. Its aim was to determine which symptoms were most common, which signs put patients most at risk of colon cancer, and how long it took patients to get a colon-cancer diagnosis.

Overall, 17 signs of early-onset colon cancer were identified.

Almost half the subjects had rectal bleeding, which was linked to a fivefold increase in early-onset colon-cancer risk, making it the largest risk factor.

About 40% had abdominal pain, the second-most-common symptom.

The third-most-common symptom was changes in bowel movements, which included constipation, diarrhea, alternating bowel habits, or alternating diarrhea or constipation. The fourth-most-common symptom in the US was diarrhea, but in studies from non-US countries, it was loss of appetite.

Patients tended to receive a cancer diagnosis four to six months after their symptoms first appeared. It's not clear whether decreasing the time to diagnosis would improve outcomes, but the risk of cancer becoming advanced increases over time, the study said.

The authors suggested that, given the prevalence of rectal bleeding and abdominal pain in colon-cancer patients, doctors should always consider the cancer a possibility before dismissing a patient with these symptoms.

The authors said there were significant differences in the studies used, which posed some challenges for analysis. They said they were unable to compare colon-cancer risk against other potential causes of symptoms, which might have provided a better picture of the relative risk.

Experts still don't know what's behind the rise in colon cancer, but ultraprocessed foods, environmental contaminants, and obesity are among the possibilities under consideration.

Dr. Michael Shusterman, a gastrointestinal medical oncologist at NYU Langone's Perlmutter Cancer Center, previously told Business Insider that to reduce the risk of developing colon cancer, he recommends patients quit smoking; cut down on alcohol; do some moderate-intensity exercise; eat more fiber and less red meat; and avoid ultra-processed foods as much as possible.

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