Colon cancer steadily increased among young people in the United States over the past two decades, with tweens enduring the most dramatic leap in cancer rates, a new study says.

The rate of colon cancer grew 500% among kids 10 to 14 between 1999 and 2020, researchers will report at the Digestive Disease Week medical meeting in Washington, D.C., later this month.

The rate also increased 333% among 15- to 19-year-olds, and 185% among 20- to 24-year-olds, researchers found.

“Colorectal cancer is no longer considered just a disease of the elderly population,” lead researcher Dr. Islam Mohamed, an internal medicine resident physician at the University of Missouri-Kansas City, said in a news release.

For the study, researchers calculated 1999-2020 trends in colon cancer for people between 10 and 44 years of age, using U.S. Centers for Disease Control and Prevention (CDC) data.

Even though the rates rose among children and young adults, they still are much lower in sheer numbers than those of older adults, results show.

Among 10- to 14-year-olds, 0.6 children per 100,000 were diagnosed with colon cancer in 2020, up from just 0.1 children per 100,000 in 1999.

Similarly, diagnoses in 15- to 19-year-olds went from 0.3 to 1.3 per 100,000, and those among 20- to 24-year-olds rose from 0.7 to 2 per 100,000.

The most common colon cancer symptoms were constipation, diarrhea, abdominal pain, rectal bleeding, and signs of iron deficiency anemia, Mohamed said.

Increases in colon cancer also occurred in older people, with rates rising:

• 71% to 6.5 per 100,000 people in ages 30 to 34.

• 58% to 11.7 per 100,000 in ages 35 to 39 .

• 37% to 20 per 100,000 in ages 40 to 44.

Risk factors for colon cancer include a family history of inflammatory bowel disease or colon cancer, Mohamed said.

Other known risk factors include obesity, tobacco use, drinking and diet. Suspected risk factors include lack of physical activity, antibiotics and dietary additives, researchers said.

Because these findings were presented at a medical meeting, they should be considered preliminary until published in a peer-reviewed journal.