The reasons behind the trends are not fully understood, but the results suggest that steady progress in reducing colon cancer incidence through screening over the past decades is stalling.
“There’s a bit of a worrying trend,” said Paul Oberstein, a medical oncologist at NYU Langone Perlmutter Cancer Center who was not involved in the study. “Something is clearly different in the younger, under-50 population, which suggests, although it’s small, that the number of cancers is increasing.”
Overall, colorectal cancer is on the decline, largely because more people over the age of 50 are being screened with colonoscopy, which can prevent cancer by detecting and removing precancerous polyps. Recently, the US Preventive Services Task Force recommended lowering the age for colorectal cancer screening to 45.
But the new report “foreshadows less favorable trends to come,” the study authors wrote, with more patients being diagnosed at younger ages and with more advanced disease. There is also an unexplained change in the incidence of “left-sided” tumours, suggesting that the biology of the disease may be changing, requiring a new approach to prevention and more research into targeted treatments.
“We know that rates are rising in younger people, but it’s alarming how quickly the overall patient population is getting younger, despite fewer numbers in the overall population,” said Rebecca Siegel, chief scientific officer at the American Cancer Society and lead author of the study. report, said in a statement. “The trend for more advanced disease in people of all ages is also surprising and should motivate everyone 45 and over to get screened.”
The overall annual incidence rate of colon cancer has fallen by 46%, from 66.2 per 100,000 people at its peak in 1985 to 35.7 per 100,000 people in 2019. Death rates have also fallen by 57% over the past 50 years, according to the report. Experts say the decline in colorectal cancer cases is largely due to a drop in smoking and the widespread adoption of colorectal cancer screening among Americans age 50 or older.
But the report, based on the latest available data available through 2019, shows gains against the disease are limited to people aged 65 and over. Here are some of the findings:
- Incidence rates have increased by 2% per year in people under 50 years of age.
- More people under the age of 50 are dying from the disease. Since 2004, mortality rates in this age group have increased by about 1% per year.
- Overall, more patients are diagnosed with regional or distant disease, meaning it has spread beyond the colon to nearby or distant lymph nodes, tissues, or organs. Incidence of regional and distant stage disease increased by about 3% per year in people under 50 years of age, while rates stabilized in people 65 years and older after a decade of slump.
- Overall, men are more at risk than women. The incidence rate of colorectal cancer was 41.5 per 100,000 in men versus 31.2 in women. The reason is likely due to differences in risk factors such as poor diet, smoking history and being overweight, according to the report.
- The disease disproportionately affects people of color. Incidence rates are highest among Alaska Natives (88.5 per 100,000), Native Americans (46 per 100,000), and blacks (41.7 per 100,000). By comparison, the incidence rate among whites is 35.7 per 100,000.
Oberstein said there is “very little understanding” of why colorectal cancer cases are on the rise in younger age groups. But other developed countries are seeing a similar trend.
Colorectal cancer is the second leading cause of cancer death in the United States. Smoking, consumption of processed meats, obesity and physical inactivity are all risk factors for the disease.
Arif Kamal, the American Cancer Society’s chief patient officer, said one of the concerns is that many people between the ages of 45 and 49 are not getting colonoscopy screening even though they are now eligible.
“There is a clear relationship” between the rate of colonoscopies and later risk of developing cancer, he said. “Screening is also therapy. If we see a precancerous polyp, we remove it.”
Kamal said there are also concerns that people in their 40s and 50s will lead less healthy lifestyles, including eating more processed foods and less fiber, than previous generations.
“As obesity rates continue to rise in the United States, we need to identify colorectal cancer as an obesity-related cancer the same way we did when we first started thinking that cancer lung was a smoking-related cancer,” Kamal said. “It will help people see that one thing leads to another.”