A landmark study has uncovered an alarming increase in cancer diagnoses among Gen X and millennials, and researchers suggest that “major exposures” may be fueling the rise.
A major new study analyzing 20 years of cancer data in the U.S. has uncovered a troubling pattern: people born in or after 1965 – including Gen X and Gen Y – are facing two to three times the risk of developing cancer compared to those born around 1955.
The findings, published in 2024, suggest that younger generations are not only more likely to be diagnosed with cancer at earlier ages, but are also carrying that elevated risk into later life, potentially leading to a lasting increase in national cancer burden.
“The last time we saw this kind of phenomenon on a global scale and with such changes was lung cancer in the mid-20th century, when it started rising from almost a rare cancer to the most common cancer,” said Timothy Rebbeck, professor of cancer prevention at Harvard , in an interview with the Harvard Gazette. “But we figured that out pretty quickly; that was cigarette smoking. In this case, we’re talking about probably major exposures or something like that.”
Higher incidence rates
The study, published in The Lancet Public Health, reviewed nearly 24 million cancer cases and over 7 million cancer-related deaths recorded between 2000 and 2019. Researchers tracked the incidence and mortality of 34 different cancer types across birth cohorts to better understand how risks are changing over time – and which cancers are rising fastest.
Out of the 34 cancer types analyzed, 17 showed significantly higher incidence rates in Gen X and millennials. The most pronounced increases were observed in cancers of the pancreas, kidneys, renal pelvis, thyroid, and small intestine.
Researchers stressed that while improved detection and diagnosis may partially explain the rise, it does not account for the full picture. The number of new cancer cases is increasing at a pace that outstrips advancements in screening, which indicates a genuine rise in disease – not just more cases being caught early.
Rising mortality
Along with diagnosis, the study also highlighted a concerning increase in cancer mortality. Among younger generations, death rates have climbed in five cancer types: liver, endometrial, gallbladder, testicular, and colorectal cancers.
These rising mortality trends suggest that younger people are not only being diagnosed more often but are also dying from certain cancers at higher rates.
Obesity
Although the study was not designed to identify exact causes, researchers noted several contributing factors already linked to early-onset cancers.
Obesity was one of the most significant. It has been associated with 10 of the 17 cancers that showed an increase, and rates of obesity have steadily climbed since the 1970s –especially among children and adolescents.
“I agree [obesity] has been posited as the leading hypothesis for why early-onset cancers have been rising globally,” said Kimmie Ng, an associate professor at Harvard Medical School, also speaking to the Harvard Gazette. “If you look at the cancer types that have been increasing in young people, they are all known to be associated with obesity.”
Other potential factors
The role of diet is another critical area of focus. Western diets – often high in added sugars, refined grains, processed foods, and saturated fats – have been linked to rising rates of colorectal and breast cancers.
However, researchers also noted that some gastrointestinal cancers not tied to obesity may be influenced by gut microbiome disruption that can be influenced by diet. This disruption is an imbalance in the gut’s natural bacteria that can lead to long-term inflammation, raise the risk of developing cancer, worsen how the disease progresses, and reduce how well treatments like immunotherapy work.
And scientists suggest it may be linked to poor diet and widespread antibiotic use early in life.
Other possible factors include exposure to environmental pollutants, sedentary lifestyles, disrupted sleep patterns, and chronic inflammation – all of which can increase cancer risk, particularly when exposure begins in childhood or adolescence.
“Research suggests that it relates to the increasing prevalence of obesity, the consumption of a Westernized diet, and leading a sedentary lifestyle,” RGA, a health-focused reinsurance group, explains in a white paper titled, “Western Lifestyle, Global Problem: Rising Rates of Cancer in the Young.” “If today’s adolescents and young adults do not change their lifestyles, the impact on rising cancer rates will be greater than ever before.”
With millions of young people potentially facing a higher lifetime risk, the urgency to find answers – and solutions – is only growing.
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