(NEW YORK) — Gen X and Millennials in the U.S. are at greater risk for 17 cancers than were previous generations, a major new study revealed.

Researchers at the American Cancer Society analyzed data from millions of people born between 1920 and 1990 who were diagnosed with 34 common types of cancer between 2000 and 2019. They also reviewed death records from the same period.

The cancers on the rise included two types of stomach cancer, small intestine cancer, estrogen receptor (ER) positive breast cancer, ovarian, liver, bile duct and colorectal cancer, uterine and testicular cancer, gall bladder, kidney and pancreatic cancer, and two types of blood cancer: myeloma and leukemia.

A subset of mouth and throat cancers in females, anal cancer in males, and Kaposi sarcoma in males were also increasingly diagnosed in people at a younger age than in previous generations, according to the study.

The cancers with the most rapidly growing incidence among younger generations are thyroid, pancreatic, kidney, small intestine, and liver cancer in females, all of which were diagnosed at rates two to four times greater for people born in 1990 compared to 1955.

Of the cancers that are being detected more frequently, nine had previously shown a decline in successive generations at some point since 1955.

Trends in cancer death rates

While death rates from most of these cancers have decreased or stabilized, younger generations are also dying at higher rates from some of them, including colorectal cancer, which is screened for in the United States.

There could be something different about the biology of cancer in younger patients, suggested William Dahut, MD, a medical oncologist and the American Cancer Society’s chief scientific officer.

“We probably need to think of different ways to screen for these cancers,” he said.

Kevin Nead, MD, a radiation oncologist and assistant professor in the department of epidemiology at MD Anderson Cancer Center, concurred: “We should actively assess and adjust screening practices for younger individuals so that we are not missing opportunities to find these cancers early and cure them,” he told ABC News, but added that screening is a complex topic and further research is needed to identify who is at greatest risk before any changes are made.

Decoding the cancer youth wave

There are various ideas behind why people are being diagnosed with cancer at younger ages.

Ten of the cancers noted in the study are associated with body weight, the researchers wrote, implying a possible link to higher obesity rates in younger generations.

“Perhaps that is a good place to [focus] efforts for people’s overall health,” Nead suggested.

But obesity is only one piece of the puzzle. The study’s authors also suggest exposures to potential carcinogens, and lifestyle habits such as processed food consumption, alcohol use, and lower physical activity levels, may negatively affect the health of younger generations more than it did previous ones.

But Dahut admitted the evidence attributing any specific factor to the findings is still murky.

“It’s almost impossible to point to one thing,” he said. “It’s so easy for us to say ‘yes, it’s obesity’; ‘yes, it’s lack of exercise’; ‘yes, it’s processed food.’ But we do not have the data to point to.”

Some bright spots in the data

Fortunately, not everything the study uncovered is bad news.

The researchers noted substantial declines in smoking-related cancers like lung cancer among young people compared to older generations. The incidence of cervical cancer is also decreasing, likely due to the success of the HPV vaccination.

While the rates of leukemia and myeloma are increasing, the rate at which people are dying from them has declined, which Nead attributed to improvements in treatments.

So, while the overall picture may be concerning, Nead cautioned that it’s important to keep the study’s findings in context.

“It’s a huge period of time and so many things changed … between 1920 to 1990,” he told ABC News, adding, “It is possible that we are just finding more cancer that may have gone undetected before.”

Screening and lifestyle changes essential

Patients should continue to prioritize cancer screening, Dahut advised, in order to minimize the risk of undiagnosed cancers. There is also ample evidence to show decreasing alcohol and tobacco use can lower the risk of cancer, he added.

“This paper doesn’t answer … what are the risk factors for cancer,” said Nead. “But a lot is related to lifestyle factors. One of the best things that you can do … for cancer and other major health issues is take consistent steps towards a healthier lifestyle, whether that’s exercise or diet or body habits.”

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