Rev. Kaitlin Sullivan — NBC News
Younger generations are at higher risk for some types of cancer, according to a new study,
Generation Xers and millennials are more likely to be diagnosed with 17 types of cancer, including nine that had declined in older adults, according to a study published Wednesday in the journal Lancet Public Health. Researchers aren’t sure why, but say obesity is likely a leading cause.
“What is happening in these generations can be seen as an indicator of future cancer trends,” said Hyuna Sung, an oncologic epidemiologist at the American Cancer Society who led the research.
Rates of colorectal cancer — one of 17 types — have been rising among younger people for decades, a worrying trend that has sparked research into other cancers.
Sung and colleagues used cancer diagnosis and mortality data from two databases — the North American Association of Central Cancer Registries and the National Center for Health Statistics — to analyze cancer trends in people born between 1920 and 1990 who were diagnosed with cancer between 2000 and 2019.
The data included 34 types of cancer, nearly 24 million diagnoses and more than 7 million deaths. To get a better look at how cancer diagnoses and death rates changed in groups of people born around the same year — called birth cohorts — the researchers grouped people by birth year into five-year intervals. For example, people born between 1920 and 1924 formed one birth cohort.
Seventeen of the 34 cancer types had an increasing incidence in younger people. The risk of pancreatic, kidney and small bowel cancer was two to three times higher in people born in 1990 than in those born in 1955. Liver cancer diagnoses in women followed the same pattern.
[Más del 40% de las muertes por cáncer en adultos de más de 30 pueden evitarse con solo cambiar algunos hábitos, dice estudio]
“The most important thing it showed us is that there is something that has changed for the group of individuals born after this time period. They have been exposed to some environmental or lifestyle factor that is causing this change,” said Dr. Andrea Cercek, a gastrointestinal oncologist at Memorial Sloan Kettering Cancer Center who was not involved in the research.
After declining for decades, these types of cancer have begun to rise again:
- Colorectal
- Endometrial
- Non-gastric
- Gallbladder
- Ovary
- Testicular
- Anal
- Estrogen receptor-positive breast cancers
- Kaposi’s sarcoma, an HIV-related cancer.
Although the study found that mortality decreased or remained stable in younger generations for most cancers, the mortality rate increased among younger age groups for endometrial, intrahepatic bile duct, gallbladder, colorectal and testicular cancers, as well as for liver cancer among women.
Endometrial cancer was the fastest growing in both diagnoses and mortality.
“It’s a sobering finding,” Sung said. “Even though many cancer rates are increasing, we don’t necessarily see this increase in mortality because we’re treating them much better than we used to.”
Many of the cancers on the rise remain rare among young people, and although rates have increased, the overall number of cases is comparatively low.
“It’s clearly happening. Almost every oncologist I know can say they see it,” Brawley added, adding that despite the alarming increases, it’s important to note that the majority of cancer diagnoses are still occurring in people over 50.
“In the 1990s, 10% of people diagnosed with colon cancer were under 50. Now it is 20%, but we must not forget the 80% who are still over 50,” he said.
[El cáncer de colon es el segundo más letal entre mujeres detrás del de seno]
Looking at people born in a specific time period can provide important clues about why certain types of cancer are increasing among younger generations.
“All of these cancers are linked to the obesity epidemic. We know that obesity is the second leading cause of cancer right now, behind tobacco use,” said Dr. Otis Brawley, Bloomberg Distinguished Professor of Oncology and Epidemiology at Johns Hopkins University, who was not involved in the new study.
About 20 percent of cancer diagnoses in the United States are linked to excess body weight, according to the American Cancer Society. Obesity rates in the country changed little in the 1960s and 1970s but rose sharply thereafter. About 13 percent of adults were obese in 1980, up from 34 percent in 2008, according to data from the Surgeon General’s Office.
Among children, obesity rates rose from 5% to 17% over the same period. Today, more than 40% of American adults and about 20% of children and adolescents are obese, according to the Centers for Disease Control and Prevention (CDC).
If obesity is the culprit, it’s likely one of several environmental and lifestyle factors that are driving this increase. Other factors could be more sedentary behavior or something in the food or water, common medications or chemical exposures or chemical agents, experts say.
Overuse of antibiotics is another possible link being looked at. Antibiotics are known to alter the gut microbiome, which has been linked to colorectal cancer. Although antibiotics are necessary to treat many bacterial infections, they are often misused and taken for problems that are not bacterial, or that do not require antibiotics.
“The list of things we can look into is very long,” Cercek said. “Antibiotics are one of the biggest culprits on the list.”
Researchers still don’t understand why certain types of cancer are on the rise among younger generations. While obesity and antibiotics are the main suspects, “we can’t rule out other exposures or chemical agents,” Brawley said.
