Why are colorectal cancer rates rising among younger adults?

Nearly double the number of young adults under 55 are being diagnosed with colorectal cancer than a decade ago, and more are dying from the disease each year, as reported recently by the American Cancer Society.

According to the study, the number of individuals in the U.S. diagnosed with advanced-stage colorectal cancer (CRC), increased by 8% from the mid 2000s, to 2019. Diagnoses of people under 55 years of age increased from 11% in 1995 to 20%, or 1 in 5 individuals. Progress against CRC also slowed, the declines in mortality of 3 to 4% each year during the 2000s, decreased to 2% during the past decade.

Medical director of the Colorectal Cancer Prevention Program at Yale Cancer Center and Smilow Cancer Hospital, Xavier Llor, MD, Ph.D., said certain lifestyle habits associated with CRC alone can't be causing this worrisome trend.

"Some factors have been identified and these increase CRC risk, especially at older ages. Obesity, sedentary lifestyle, the Western diet, and high sugar intake would only explain a fraction of these cases," said Dr. Llor, who is also a Professor of Medicine (Digestive Diseases) at Yale School of Medicine.

Historically, Dr. Llor says, we have known that a substantial number of individuals diagnosed at a young age were due to genetic defects causing cancer-predisposing syndromes such as Lynch syndrome. This most recent significant increase in CRC among the younger population, he says, is more associated with a patient's environment, including all sorts of exposures, and diet. However, Dr. Llor said more research needs to be done.

"Genetic syndromes are also more commonly the cause for younger CRC patients than older ones, but these remain quite stable over the years and can't explain a sudden raise in cases as we have seen in the last two decades," said Dr. Llor. "It will likely boil down to environmental, dietary factors that we have not quite identified yet to explain many of these cases."

Dr. Llor pointed out how colorectal cancer continues to disproportionally affect certain ethnic groups more.

"CRC incidence is highest in people who are Alaska Native (88.5 per 100,000), American Indian (46.0 per 100 thousand), or Black (41.7 per 100,000; versus 35.7 per 100,000 in Whites) during 2015 to 2019, likely reflecting differences in risk factor prevalence, such as excess body weight, processed meat consumption, historical smoking," said Dr. Llor.

With screening recommendations for adults beginning at age 45, Dr. Llor urges adults to talk to their doctors about scheduling a screening, a decision he says could save their life. If someone has a parent, sibling, or child with CRC, screening should start at age 40 and in some cases even sooner.

"Since the endorsement of the Unites States Preventative Services Task Force to start colorectal cancer screening for average risk at 45, we have seen a significant increase of individuals in the 45 to 49 age group being referred for CRC screening. The majority though are still not screened, so there is a lot of work to be done in this age group. The 50 to 54 age group is also a target group as their screening rates barely reach 50%," said Dr. Llor.

Although this new data on CRC is concerning, Dr. Llor says you should focus on what you can control to lower your risk: refraining from smoking and reducing your intake of alcohol and processed foods.

"We stress lifestyle modifications that can actually help prevent the development of that cancer," said Dr. Llor. "Decreasing your body weight, even a small amount, can make a big difference in terms of cancer risk. The type of food that we are eating makes a big difference. Less red meat, more vegetables, and fruits. All of those things do have a very important impact," said Dr. Llor.