People born in the 1990s face at least four times the risk of early-onset colorectal cancer compared to people born in the 1960s, according to a study published in the Journal of the National Cancer Institute that drew on long-term cancer incidence data from Australia, Canada, England, and the United States. That number represents one of the starkest generational gaps in cancer risk ever recorded. Yet for years, the prevailing explanation – better screening, better detection – kept falling short. Doctors were finding cancers in people who had no family history, no obvious risk factors, and no reason to have been screened in the first place.
The scale of what’s happening has quietly reshaped oncology wards. Clinicians who once rarely saw a patient under 40 with a gastrointestinal cancer are now reporting that early-onset cases make up a significant and growing share of their caseloads. One oncologist described the shift as “truly stunning.” The patients are their own age, or younger. And unlike the generational decline in cancer deaths that defined the last three decades of medicine, this trend is moving in the wrong direction.
Now, a major piece of the puzzle may have fallen into place. Research published in June 2026 in Nature Medicine by scientists at Washington University School of Medicine in St. Louis found that people born in the 1980s and 1990s are biologically older than their parents and grandparents were at the same chronological age – and that faster biological aging is associated with a measurably higher risk of developing cancer before 55.
The Biological Age Gap Behind Rising Cancer in Young Adults
A new study led by researchers at WashU Medicine suggests younger generations are aging biologically faster than their older counterparts, and this faster biological aging was linked to early-onset cancers. The distinction between biological age and chronological age matters here. Chronological age is simply how many years a person has lived. Biological age is different: it reflects how old the cells, tissues, and organ systems appear to be based on measurable molecular signals, regardless of what the calendar says.
Given the increasing prevalence of cancer in younger generations, researchers at Washington University School of Medicine in St. Louis conducted an observational cohort study that included 154,169 young adults from the UK Biobank and 10,262 participants from the United States All of Us Research Program. In plain terms, a 35-year-old millennial’s body may be functioning more like that of someone significantly older, and that accelerated wear appears to carry a measurable cancer penalty.
The larger the gap between biological age and chronological age, the higher the cancer risk, according to the researchers. They found that people in more recent birth cohorts had larger age gaps than those in older birth cohorts, which may help explain the rise in early-onset cancer in recent generations. For each incremental increase in the measure of biological aging, the risk of developing an early-onset solid cancer increased by about 8%.
The study led by researchers at Washington University School of Medicine in St. Louis identified a direct link between accelerated biological aging and an increased risk of cancers diagnosed before age 55. The study also found that faster aging increased cancer risk among certain organ systems in younger adults. For example, advanced immune aging was associated with early-onset lung cancer, while accelerated aging of fat tissue was linked to early colon cancer. Importantly, the researchers were careful to note that this association does not prove causation. As Dr. John Riches, a clinical reader in cancer immuno-metabolism at Barts Cancer Institute, put it: “This study offers an important new clue as to why we are seeing more cancers diagnosed in younger adults… importantly, this study does not show that faster biological aging directly causes cancer, but it provides a strong basis for further research.”
How Large Is the Problem?
A large study led by researchers at the American Cancer Society suggests incidence rates continued to rise in successively younger generations in 17 of the 34 cancer types studied, including breast, pancreatic, and gastric cancers. Mortality trends also increased in conjunction with the incidence of liver cancer in females, uterine corpus, gallbladder, testicular, and colorectal cancers. The study was published in The Lancet Public Health. The ACS-led research analyzed cancer incidence data from more than 23.6 million patients diagnosed with 34 types of cancer between 2000 and 2019, with mortality records from more than 7.3 million deaths also examined.
Globally, the trajectory is equally sobering. In 2019, the global incidence of early-onset cancers exceeded 3.26 million cases, marking a 79.1% increase since 1990. Deaths from early-onset cancer rose by 27.7% over the same period. In the United States specifically, an estimated 2 million new cancer cases and 611,720 cancer-related deaths were expected in 2024. By 2026, a study published in a National Institutes of Health journal projects that figure has risen to more than 2.1 million new diagnoses annually.
Gastrointestinal cancers alone account for 39% of global cancer-related deaths, and within that group, the youngest patients are increasingly bearing a disproportionate share of new diagnoses. Among the cancer types rising fastest in younger generations are pancreatic and gastric cancers, alongside the cancer type now commanding the most clinical attention: colorectal.
For more on which specific cancer types are surging fastest across generations, this breakdown of 17 rising cancers in Gen X and millennials covers the American Cancer Society’s full findings.
Colorectal Cancer: The Defining Crisis of a Generation
No single cancer illustrates the early-onset trend more sharply than colorectal cancer. The American Cancer Society’s annual report noted a shift in the burden of cancer incidence from older adults to younger adults, and from men to women. For colorectal cancer specifically, incidence rates among older adults have dropped by about 1% per year between 2012 and 2021, but rates increased by 2.4% per year over the same period in those younger than 50.
Although cancer remains most common among older adults, cancer rates have recently begun to grow significantly among younger adults, leading to concerns from health experts across the country. By 2030, about 15% of colorectal cancer cases will be diagnosed in younger adults. All countries studied showed increasing early-onset colorectal cancer incidence in successive birth cohorts since 1960, with cohort effects observed across all countries, with sharper increases at younger ages.
In January 2026, the American Cancer Society reported that colorectal cancer is now the leading cause of cancer death for people under the age of 50 in the United States. Projections from Facing Our Risk of Cancer Empowered suggest colorectal cancer will retain that grim distinction through at least 2030. The rectal cancer subset of this trend is especially stark: a 2026 NBC News report found that rectal cancer deaths are rising two to three times faster than colon cancer deaths among younger adults.
Early-onset colorectal cancers also tend to behave more aggressively than those diagnosed in older patients. Early-onset colorectal cancer often presents at advanced stages and has a significantly worse prognosis than colorectal cancer diagnosed in older patients.
What’s Driving the Biological Aging Clock Forward?
Researchers have linked the rise in early-onset cancer to factors ranging from obesity and diet to environmental exposures, but no single explanation has fully accounted for the trend. The WashU Medicine biological aging study points toward a combination of forces that, taken together, appear to be accelerating cellular damage in ways previous generations did not experience at the same scale or age.
Gut health is one prominent thread. Ten of the 17 cancers with increasing incidence in younger birth cohorts are obesity-related, including colorectum, kidney and renal pelvis, gallbladder, uterine corpus, pancreas, and estrogen receptor-positive breast cancer, suggesting a potential role of obesity in emerging cancer trends in recent generations. A 2025 study published in the Journal of Personalized Medicine found that gut microbial dysbiosis – an imbalance in the community of bacteria and microbes that live in the digestive tract – is implicated as a key driver in early-onset colorectal cancer. The gut microbiome plays a critical role in immune regulation, inflammation control, and cellular signaling. When that balance is disrupted, cells lining the colon may face the kind of chronic stress that accelerates biological aging.
Environmental chemical exposures represent another significant concern. PFAS, or per- and polyfluoroalkyl substances, are synthetic chemicals used since the 1950s in everything from non-stick cookware and food packaging to stain-resistant carpets and firefighting foam. Because the carbon-fluorine bond is one of the strongest in chemistry, these chemicals do not degrade easily in the environment, earning them the nickname “forever chemicals.” Research from Memorial Sloan Kettering Cancer Center notes that prenatal exposures, environmental toxins, and various lifestyle factors may all be contributing to the rise. PFAS have been linked to higher rates of testicular and kidney cancer, two of the types showing the steepest generational increases.
Microplastics have drawn growing scientific attention as well. Microplastics have been found in human and animal tissues including lung, liver, placenta, and arteries. According to Dana-Farber Cancer Institute, microplastics have been shown to disrupt the balance between microbes and the mucus lining of the gut, potentially exposing cells to harm, and to carry toxic pollutants with cancer-related properties. Research published in 2025 found that microplastics can damage DNA, disrupt cell division, and cause chronic inflammation, a well-established driver of cancer development.
Researchers around the world are currently exploring potential environmental, lifestyle, and societal risk factors and mechanisms that may contribute to accelerated aging and related cancer risk in younger generations. The honest answer is that this is almost certainly a multi-factor problem, with biology, chemistry, diet, and behavior all interacting in ways that compound the risk.
Breast Cancer in Young Women
The breast cancer picture follows a similar trajectory. The incidence of breast cancer has risen globally among individuals under 50, particularly affecting women. According to the Breast Cancer Research Foundation, breast cancer incidence in women under 50 rose approximately 1.4% each year between 2012 and 2022. Younger women tend to experience more aggressive forms of breast cancer and worse outcomes compared to their older counterparts, partly because younger tumors are more likely to be hormone-receptor-negative, a type that responds less readily to standard hormonal treatments.
The generational biology explanation applies here too. Obesity, sedentary lifestyle, alcohol use, and delayed or reduced childbearing have all shifted across generations in ways that raise baseline breast cancer risk. As cancer rates in younger adults rise, with each successive generation facing higher risks than the one before it, researchers are asking whether cellular damage is accumulating faster in recent generations – and the WashU Medicine study provides evidence that younger generations are indeed aging faster biologically than their older counterparts. Accelerated biological aging may be the common denominator tying these exposures together into a measurable, generational cancer signal.
Read More: Appendix Cancer Is Tripling in Millennials – And No One Knows Exactly Why
What This Means for You
The US Preventive Services Task Force recommends that adults age 45 to 75 be screened for colorectal cancer, according to the CDC – a threshold lowered from the previous starting age of 50. The American Cancer Society’s 2026 guidelines reaffirm that average-risk adults should initiate colorectal cancer screening at 45 and continue through 75. If you have a family history of colorectal cancer, inflammatory bowel disease, or any first-degree relative diagnosed before 60, talk to your doctor about starting earlier.
The WashU Medicine study suggests that measures of accelerated aging could help identify individuals at higher risk of early-onset cancer and guide new strategies for cancer prevention and early detection. In the meantime, the actionable steps that slow biological aging are the same ones that reduce cancer risk across the board: regular physical activity, a diet centered on whole foods and fiber, limited alcohol, avoiding tobacco, and minimizing exposure to known chemical carcinogens where possible.
Symptoms that once seemed too mild to report are worth taking seriously now. Persistent changes in bowel habits, unexplained weight loss, blood in the stool, and ongoing abdominal discomfort are all reasons to see a doctor rather than wait. The evidence is clear that for cancer in young adults, early detection is still the most powerful tool available, and that window is only as wide as the conversation you’re willing to have with your physician.
Disclaimer: This information is not intended to be a substitute for professional medical advice, diagnosis, or treatment and is for information only. Always seek the advice of your physician or another qualified health provider with any questions about your medical condition and/or current medication. Do not disregard professional medical advice or delay seeking advice or treatment because of something you have read here.
AI Disclaimer: This article was created with the assistance of AI tools and reviewed by a human editor.