• A new study investigates trends in 34 types of cancer in the United States.
• For 17 cancer types, Generation X and Millennials have a higher risk than previous generations.
• Similarly, for five cancer types, mortality risk is also higher in younger generations.
• Many factors may be involved, but obesity likely plays a substantial role.

A new study published August 1 in The Lancet Public Health takes an in-depth look at cancer rates in the United States. The scientists measured incidence rates of cancer and cancer mortality in different generations.

They found that 17 cancer types were more common in recent generations, noting the incidence rate for some forms was 2–3 times higher in people born in 1990 than in 1955.

While the causes for these increases require more research, the authors cite obesity, diet, and environmental toxins as major contributing factors.

Higher cancer rates in younger generations

In a previous study published in 2019 by the same authors, they found the incidence of eight types of cancer increased in younger generations compared with older generations.

However, no study has looked at both cancer incidence — the number of new cases — and cancer mortality by birth year. The latest study plugs this gap.

As the authors explain, trends in cancer incidence in people aged 50 or younger mostly reflect an increased exposure to carcinogenic factors in early life or young adulthood.

So, they “foreshadow future disease burden as these young cohorts carry their increased risk into older age, when cancers most frequently occur.”

Increases in cancer incidence and mortality

To investigate, the scientists used information from 23,654,000 people diagnosed with 34 types of cancer and 7,348,137 deaths from 25 cancers from 2000–2019.

They found an increased incidence in 17 of the 34 cancers in progressively younger generations:

• cardia gastric: a type of stomach cancer
• small intestine
• estrogen receptor-positive breast
• ovary
• liver and intrahepatic bile duct (in females)
• non-HPV-associated oral and pharynx (in females)
• anus (in males)
• Kaposi sarcoma (in males): a form of cancer that starts in the lining of blood and lymph vessels
• colorectal cancer
• endometrial cancer
• gallbladder and other biliary
• kidney and renal pelvis
• pancreas
• myeloma: a blood cancer
• non-cardia gastric: another type of stomach cancer
• testis
• leukemia: a blood cancer

The increase in incidence was particularly pronounced in cancers of the small intestine, thyroid, kidney and renal pelvis, and pancreas. Compared with people born in 1955, the incidence in those born in 1990 was two- to three-fold greater.

Also, in five cancer types, mortality rates also increased:

• liver and intrahepatic bile duct in females
• endometrial cancer
• gallbladder and other biliary
• testicular
• colorectal cancers

“These findings are sobering as they indicate the increased cancer risk in younger generations is not merely an artifact due to more frequent cancer detection and diagnosis,” explained study author Hyuna Sung, PhD.

“Instead, it points to a genuine increase in cancer risk at the population level, with the increase in incidence being substantial enough to outweigh improvements in cancer survival,” Sung told Healthline.

Why the sharp increase in cancer rates?

While this study was not designed to explain why these cancers increased, the researchers explain that obesity likely plays a substantial role.

10 of the 17 cancers listed in the study are associated with obesity. The authors explain that, since the 1970s, obesity has increased in all age groups, but the swiftest increase has been in younger people, aged 2–19 years.

This is backed up by other research demonstrating that excess weight and obesity at a younger age are associated with an increased risk of 18 forms of cancer.

According to the new paper, beyond overweight and obesity, other factors may also play a role, such as an increase in sedentary lifestyles, altered sleep patterns, and chemicals in the environment. However, much less is known about the importance of these factors.

How diet and the gut microbiome may affect cancer rates

The so-called Western diet, which is high in saturated fats, sugar, refined grains, and ultra-processed foods, is linked to increased cancer risk.

“Emerging evidence suggests that ultra-processed food increases body weight but is also independently associated with the risk of some cancers, such as breast and colorectal,” Sung said.

Because some cancers affecting the digestive system are not related directly to obesity, the authors suggest that changes in the gut microbiome may also be a factor.

With the two-pronged rise of the Western diet and antibiotic use, the gut microbiome has been severely impacted.

Although scientists do not fully understand the role of gut bacteria in cancer, the authors write that specific microbes and dietary patterns have now been linked to oral and gastrointestinal tract cancers.

How is epigenetics related to cancer?

Jennifer Dunphy, DrPH, co-founder of the Wellness Innovation Network, told Healthline she was particularly interested in the potential role of epigenetics on health.

“Epigenetic changes are changes to the expression of proteins from DNA, without changes to the DNA itself — usually as a result of environmental factors,” she explained. In other words, when an individual passes on their genes to their offspring, they also pass on certain changes to how these genes are expressed — how easily they are turned “on” or “off.”

“It seems that epigenetic changes are a large part of the equation here, meaning your DNA isn’t the only thing that matters — your behavior today is probably going to impact your offspring through heritable changes, just like the behavior and exposures of your parents and even your grandparents impact your health today,” Dunphy said.

This adds a fresh and rather bleak twist to the findings.

“While there are many harmful exposures we can and should prevent against,” Dunphy continued. “I do not think that, on average, we are doing all of this extensive damage to our bodies in one lifetime alone, I think we are carrying over vulnerabilities from our predecessors.”

Exposure to toxins may affect cancer rates

The authors suggest that certain environmental toxins may play a role in increasing cancer rates.

“The most harmful environmental toxin thought to contribute to carcinogenesis is the use of plastics and their breakdown products,” Walter Kim, MD, an integrative medicine physician with Brio-Medical, told Healthline. Kim was not involved in the study.

Dazhi Liu, PharmD, an oncology clinical pharmacy specialist and medical contributor for Drugwatch, not involved in the study, suggested other potential candidates, including:

• aflatoxins
• benzene
• soot
• arsenic
• aristolochic acids
• nickel compounds
• radon
• thorium
• trichloroethylene
• vinyl chloride
• wood dust

Rates of some forms of cancer are declining

Despite the concerning implications of increasing cancer rates in younger generations, Sung noted a few silver linings.

“The accelerated downturn in the trend of cervical cancer incidence shows the effectiveness of HPV vaccination among women born around 1990, who were about 16 years old when HPV vaccination was first approved in the United States,” she said.

Sung added the recent decline in cancers of the lung, larynx, and esophagus was driven by the drop in smoking rates.

Mortality rates are also declining for many cancer types, even those with increased rates. This, the scientists believe, is likely due to early detection due to better screening, advances in treatment, or both.

“The five-year survival rate for pancreatic cancer in young adults increased significantly from 16.5% in 2000 to 37.2% in 2016,” Liu told Healthline.

Sean Devlin, MD, chief medical officer for Brio-Medical, not involved in the study, told Healthline the silver lining is awareness.

“Further work and funding for earlier screening should be instituted in an effort to catch these diseases in a timely manner so that they can be adequately treated with the tools that we have,” Devlin said.

Takeaway

The incidence rate of 17 cancers and the mortality rate of five cancers is higher in Gen Xers and Millennials than in older generations, a new study reported. These increases are probably due to overweight, obesity, the Western diet, changes in the gut microbiome, and environmental toxins.