Gen X, millennials more likely to get cancer, new study shows

• The study from the American Cancer Society found adults in their 30s, 40s and 50s are more likely than previous generations were to develop 17 different types of cancers, including breast, liver and pancreatic cancers.
• Previous research has indicated alarming increases in certain cancers among younger adults, such as colorectal cancer.
• A National Cancer Institute study published in June concluded Gen Xers were more likely to be diagnosed with cancer as they aged than previous generations, NPR reported in June.

What they're saying: "It's really sort of scary to see all in one dataset," said Andrea Cercek, co-director of the Center for Young Onset Colorectal and Gastrointestinal Cancers at Memorial Sloan Kettering Cancer Center.

• "But it definitely reflects what we've known and what we've noticed as well in our clinics," said Cercek, who wasn't involved in the study. "We really have no idea why."

What they found: The study used data from 23.7 million patients dating back to 1920 through 1990 to classify people based on their birth year because they're more likely to share social, economic and environmental factors during key developmental years.

• Of 34 cancers examined, half had increased incidence among younger adults, according to the study published Wednesday in The Lancet.
• Incidence of eight different cancers increased with each successive age cohort after 1920.
• In particular, adults born in the 1990 cohort were two or three times more likely to get cancers of the small intestines, kidney and pancreas (as well as the liver and bile duct in women) compared with those in born in the 1955 cohort at the same age.

Zoom in: In the case of five cancers — liver and endometrial in females, as well as gallbladder, testicular, and colorectal cancers — young adults were more likely to die compared with prior generations.

• That's particularly concerning because it's "despite the fact that we have much better drugs for a lot of them," ACS chief scientific officer William Dahut told Axios.

Reality check: Cancer is still far more likely to occur in older adults, with the median age of a cancer diagnosis in the U.S. at 66 years old, per the NCI.

• "It's still a much lower risk to have cancer in a young adult than someone over the age of 50," Dahut said.

• "However it can occur, and if you have a persistent symptom, and someone tells you, 'Well, you're too young for cancer,' that's not true."

Between the lines: Sedentary lifestyles and increased obesity may be key contributors to rising cancer incidence in younger generations. Ten of the 17 cancers with increased incidence are obesity-related, Dahut pointed out.

• But the picture is likely more complicated.
• For instance, colorectal cancer is considered an obesity-related disease. But the historical rise in obesity doesn't always track with the uptick of disease in young people, Cercek said.
• Additionally, she said, doctors report commonly seeing younger colorectal cancer patients who are active and at a healthy weight.

What to watch: Researchers are investigating potential environmental factors, such as exposure to carcinogens in food or antibiotic use, as well as lifestyle changes, including increased alcohol use.

• Ultraprocessed foods and the use of PFAS, known as "forever chemicals," are also being studied.
• But Dahut says genetic predisposition could be a key factor as well as early environmental exposures.

What to watch: The study could have implications for how doctors practice and for cancer screening.

• It could drive a push toward more at-home testing for cancer and increase patient responsibility for understanding their personal risk and pursuing screening accordingly, Dahut said.
• One other potentially related trend to watch: how much anti-obesity medications impact risk for cancer and change future trends, Dahut said.