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WASHINGTON -- Though overall numbers remain very low, annual colorectal cancer (CRC) rates in the U.S. have more than tripled among teenagers over the past two decades, coinciding with increases across all younger age groups, an analysis of the CDC Wonder Database found.

From 1999 to 2020, annual CRC rates among children ages 10-14 jumped by 500% (reaching 0.6 per 100,000 in 2020), while rates rose by 333% in teens ages 15-19 (1.3 per 100,000) and by 185% among adults ages 20-24 (reaching 2 per 100,000), reported Islam Mohamed, MD, of the University of Missouri-Kansas City, in a presentation at the annual Digestive Disease Week (DDW) conference.

"The trend is consistent, and it's in all age groups" that were analyzed, Mohamed told MedPage Today. "But the absolute incidence is not high enough to blanket-generalize screening measures for the whole population."

For other age groups, the level of increase and incident rates for 2020 were as follows:

• 25-29 years: 68%, reaching about 3 per 100,000
• 30-34 years: 71%, reaching 6.5 per 100,000
• 35-39 years: 58%, reaching 11.7 per 100,000
• 40-44 years: 45%, reaching 21.2 per 100,000

A trend of rising CRC cases in younger people prompted the U.S. Preventive Services Task Force to recommend CRC screening starting at age 45 instead of 50 for individuals at average risk. Last year, an American Cancer Society study found that the proportion of all new CRC diagnoses that are in patients younger than 55 grew from 11% in 1995 to 20%, and new cases rose by 2% annually among people younger than 50.

Statistical trends like these inspired Mohamed and colleagues to study CRC statistics by age group, he said. The researchers had also followed media reports about younger celebrities with CRC, including the late "Black Panther" actor Chadwick Boseman, who died at age 43.

Mohamed said his clinic has seen multiple cases where young patients have come in with symptoms like bleeding and mistaken them for conditions like hemorrhoids instead of CRC "because they're not aware of symptoms of cancer."

"Eventually, once they get a scope or colonoscopy, we find that there's something else that is going on," he said.

Mohamed cautioned that incidence rates are still much lower in the under-45 population than in older groups. From 2012-2016, the incident rate per 100,000 was 59.5 for people ages 50-54 and 153 for those ages 70-74, according to the .

Possible explanations for the rise in cases include increasing rates of obesity and metabolic syndrome, Mohamed said. Alcohol use and smoking can also play roles, he said, along with diet -- especially processed red meat consumption -- and sugar-sweetened drinks.

The findings emphasize that the general public, even younger populations, needs to take the signs and symptoms of cancer seriously, Mohamed said. "It's very important that they are aware that when they have abdominal symptoms with no reason, they should be evaluated. And they should be concerned if they have constipation, diarrhea, or changes in bowel habits."

As for physicians, they should carefully evaluate patients who show indications of cancer, he said.

The University of Kentucky's Syed Adeel Hassan, MBBS, MD, who's familiar with the new findings but did not take part in the research, told MedPage Today that the study is "tremendous." The findings "further provide a detailed breakdown of young-onset CRC incidence for various young age groups below the age of 45 years," Hassan said. "However, this is just the tip of the iceberg and further work is needed to broaden the applicability of these results."

Hassan, who led a study presented at DDW that highlighted low declines in CRC mortality rates in Appalachian Kentucky compared with the rest of the country, said "these trends in rising incidence in younger people are not well understood."

"Modifiable lifestyle risk factors and social trends may be the actual culprit." In particular, he said, diets high in saturated fats and red meats have been linked to a 10-fold increase in the risk of developing CRC.

"Physical inactivity is also a risk factor for CRC," he said. "This can be further explained by the expansion of sedentary jobs by up to 80% in the past few decades."

For now, Hassan said, "clinicians must be wary of young-CRC predominant symptoms such as abdominal pain and raise the bar for clinical suspicion for potential CRC screening in the young population."

Moving forward, Hassan said, "the rising burden of young-onset CRC will likely force GI societies to amend recommendations for CRC screening."

The next steps are to "identify mortality-related trends," he said. "Furthermore, the influence of COVID on CRC and its associated risk factors must be ascertained in the at-risk young population." And, he added, better understanding of incidence rates by county and state, urban-rural classification, gender and race would be "instrumental to develop well-characterized predictive factors for young-onset CRC."

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