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 significantly 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 significantly since the mid-1990s. Between 2011 and 2019, rates increased by 1.9% a year in people younger than 55, with the biggest uptick in people in their late 20s to early 30s , according to existing research by The American Cancer Society.

However, colon cancer deaths in younger patients are still rare compared with older people. From 1999 to 2020, patients below the age of 55 accounted for 138,652 of the total 1,166,158 colon cancer, or 11.8%, according to a 2023 study.

Colon cancer symptoms, such as weight loss and appetite changes, can be indicative of many illnesses, the authors of the news study published May 24 in JAMA Network wrote. This means they're often missed, leading to late-stage diagnosis , which is harder to treat.

To combat this, researchers used data from 81 studies across six countries involving nearly 25 million people under 50 with early-onset colon cancer . Their 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 of the participants had rectal bleeding, which was linked to a five-fold increase in early onset colon cancer risk, making it the largest risk factor.

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

Changes in bowel movements was the third, and 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, the study said.

Patients tended to receive a cancer diagnosis between 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 it before dismissing a patient with these symptoms.

There were significant differences in the studies used, which posed some challenges for analysis, the authors 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, they said.

Experts still don't know what's behind the rise in colon cancer, but ultra-processed foods , environmental contaminants, and obesity, among other things, are being considered possible causes.

Dr. Michael Shusterman, a gastrointestinal medical oncologist at NYU Langone's Perlmutter Cancer Center on Long Island, 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.