Colorectal cancer rates have been rising for decades among people too young for routine screening, new research finds.

Routine screening is recommended every 10 years starting at age 45; the new study focused on rates of the disease in children and adults ages 10 to 44, using data from the Centers for Disease Control and Prevention.

Cases of colorectal cancer were on the rise in all age groups, the researchers found.

“It means that there is a trend,” said Dr. Islam Mohamed, an internal medicine resident physician at the University of Missouri-Kansas City who led the research. “We don’t know what to make of it yet, it could be lifestyle factors or genetics, but there is a trend.”

The findings, which have not yet been published in a peer-reviewed journal, will be presented later this month at the Digestive Disease Week conference in Washington, D.C. 

Despite the increases, the overall number of cases in people younger than 40 was still low. In people under age 30, cases remained exceedingly rare.

But with such low rates to begin with, any increase can take on a larger significance.

The study found that colorectal cancer diagnoses in children ages 10 to 14 jumped from 0.1 cases per 100,000 in 1999 to 0.6 per 100,000 in 2020, a 500% increase. Cases among 15- to 19-year-olds jumped by more than 300%, from 0.3 per 100,000 to 1.3 cases per 100,000 people. In people ages 20 to 24, cases rose from 0.7 to 2 per 100,000 people, a 185% rise. 

“When you are starting off with a very rare disease in 15-year-olds and you add a couple cases, you are going to have a huge percentage increase,” said Dr. Folasade May, an associate professor of medicine in the University of California, Los Angeles Vatche and Tamar Manoukian Division of Digestive Diseases. 

The increases were smaller for people over 25, but they also started with higher rates in 1999 than the younger groups. People older than 25 saw a more moderate, but still significant, rise in cases. The age group that was just too young to be routinely screened — those ages 40 to 44 — saw an increase of 45%, from about 15 per 100,000 people to about 21 cases per 100,000 people in 2020.

“We know this disease is age-related, as you get older you are more likely to develop polyps and those polyps are more likely to develop into cancer,” said May. 

May said that although the overall trend is alarming, it’s reassuring to see that the oldest group had the smallest percentage increase, since that group started with the largest number of cases. The data is still important, she said.

“Anybody who is 15 to 19 years old getting a colorectal cancer diagnosis is bad,” May said. 

‘Changing the face of colorectal cancer’

Colorectal cancer rates have been rising in people younger than 50 over the last few decades. At the same time, cases and deaths from the cancer that was once thought to only affect older people is decreasing in people in their 60s and beyond. 

“This reflects the changing face of colorectal cancer,” said Dr. Christopher Lieu, co-director of gastrointestinal medical oncology at the University of Colorado School of Medicine.

The increasing rates in younger people means that the greater risk for the disease will likely stick with them for the rest of their lives, a phenomenon called the birth cohort effect, Lieu said.  That means that a 40-year-old born in 1984 has a higher risk of colorectal cancer than someone born in 1950 did when they were 40.  

“It’s not like when you become a 50-year-old that risk diminishes, you carry that risk with you,” he said. “As younger people age, I worry that we will see increases in colorectal cancer cases in the groups that are getting screened.”

Doctors are still searching for answers as to why colorectal cancer cases are on the rise among younger generations. But the reason does not appear to be genetic, May said. 

“There are a few cancers where we are now seeing an earlier onset and they are probably linked. We don’t know why, but I think what we all agree on is that it is something environmental over something genetic,” she said, noting that it may be tied to more recently developed food processing methods or exposure to plastics. 

The experts agreed that the increases in colorectal cancer rates among younger generations were alarming, but did not support lowering the screening age for people who have an average risk. In 2018, the American Cancer Society dropped its recommendation for routine screening from age 50 to 45. 

“Before we talk about lowering the screening age from 45, we need to get those people screened. Less than 60% of people 45 and over have been screened,” May said. 

Lieu said the data reinforces the importance of everyone, in every age group, being aware of the warning signs of colorectal cancer, and that doctors understand the importance of screening even their young patients if symptoms arise. 

“Young patients wait longer to go to the doctor and also have to wait longer to establish their diagnosis because many of our patients get told they are too young to have colorectal cancer,” Lieu said. “We don’t want our patients to experience that any more, especially based on this data.” 

The most common symptoms patients in the study diagnosed with early onset colorectal cancer reported were changes in bowel habits — either constipation or diarrhea — abdominal pain, rectal bleeding and signs of anemia. Lieu said if anyone, especially a young person, has blood in their stool, that is reason to schedule an appointment with a doctor. 

One of the most powerful things a person can do for their health is to understand their family history, Mohamed said. 

“Knowing their family history can provide them with valuable insights into their own health,” he said, noting that people who have a family history of colorectal cancer should start getting screened 10 years before a sibling or parent was diagnosed.