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

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, according to existing research by The American Cancer Society. Although 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 data.

But 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, said 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.