Younger generations at increased risk for several cancer types
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Key takeaways:
- Incidence rates of multiple cancer types are higher among Gen X and Millennial populations than older generations.
- Underlying risk factors must be identified and addressed.
Incidence rates for 17 different cancer types increased for successively younger generations in the United States during the past century.
Individuals born around 1990 had two to three times higher incidence of small intestine, kidney and pancreatic cancers as those born around 1955.
“Despite many unknowns, emerging evidence suggests that early-lifetime exposures to well-established cancer risk factors such as obesity, sedentary lifestyle and unhealthy diet increase the risk for early-onset cancers,” Hyuna Sung, PhD, senior principal scientist at American Cancer Society, told Healio.
Background and methods
Prior research by Sung and colleagues showed increasing incidence rates of eight cancer types — including six malignancies associated with obesity — in successively younger generations, according to study background.
Another investigation found individuals in Generation X — those born between 1965 and 1980 — may have higher incidence of multiple cancers, including leukemia and colorectal, thyroid, uterine and kidney cancers.
In the current study, Sung and colleagues used registry data to evaluate incidence and mortality rates for the 34 most common types of cancer among adults aged 25 to 84 years between 2000 and 2019.
Researchers used the North American Association of Central Cancer Registries and SEER to identify 23.65 million individuals diagnosed with cancer, as well as 7.34 million people who died due to one of 25 cancer types.
For their cross-generation comparison, Sung and colleagues evaluated birth year cohorts established at 5 year intervals between 1920 and 1990.
Results and next steps
Compared with the 1955 cohort, people born around 1990 had significantly higher incidence rates of small intestine (incidence rate ratio [IRR] = 3.56; 95% CI, 2.96-4.27), thyroid (IRR = 3.29; 95% CI, 2.91-3.73), kidney and renal pelvis (IRR = 2.92; 95% CI, 2.5-3.42), and pancreatic (IRR = 2.61; 95% CI, 2.22-3.07) cancers.
Compared with women in the 1955 birth cohort, women in the 1990 cohort had increased incidence of liver and intrahepatic bile duct cancers (IRR = 2.05; 95% CI, 1.23-3.44), and those in the 1985 cohort had greater incidence of non-HPV-associated oral or pharyngeal cancers (IRR = 1.26; 95% CI, 1.14-2.61).
IRRs for nine other cancers — which had declined in older birth cohorts — increased among younger cohorts. These cancers included estrogen receptor-positive breast cancer, uterine corpus cancer, colorectal cancer, noncardia gastric cancer, gallbladder and other biliary cancer, ovarian cancer, testicular cancer, and anal cancer and men with Kaposi sarcoma (P < .05).
IRRs for all cancer types in the 1990 cohort were 12% to 169% higher than those observed in the birth cohort with the lowest incidence.
Carcinogenic exposures early in life or during young adulthood may be contributing to rising incidence of many cancer types, researchers wrote. In addition, 10 of the 17 cancers with higher incidence among younger birth cohorts are related to obesity, according to researchers.
“Investing in education for health promotion and improving the built environment and school food systems for children and adolescents is crucial to reducing the risk for cancer and other chronic diseases,” Sung said. “Quality education equips young people with the knowledge and skills to make healthier lifestyle choices, while a well-designed built environment encourages physical activity by providing safe spaces for exercise and play. Additionally, a nutritious school food system ensures that children have access to healthy meals, fostering better eating habits from a young age. The importance of educating the harms of alcohol consumption and smoking cannot be overstated.”
Mortality rate ratios increased in younger birth cohorts for uterine corpus, testicular, colorectal, gallbladder and other biliary cancers, as well as for liver and intrahepatic bile duct cancers specifically among women.
“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,” Sung said. “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.”
Researchers noted the “major” limitation of their study as the “identifiability issue that is inherent to all age-period-cohort modeling studies, where changes in disease incidence cannot be separately attributed to each element because of their co-linear nature,” they wrote.
“Epidemiologic studies are necessary to address significant gaps in our understanding of how risk factor exposures during early life — starting from adolescence, childhood, infancy, and even prenatal stages — relate to cancer risk throughout life,” Sung said. “Focus should be placed on potentially modifiable risk factors, such as environmental and lifestyle factors, to guide preventive strategies.”
For more information:
Hyuna Sung, PhD, can be reached at hyuna.sung@cancer.org.
Perspective
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Laleh Melstrom, MD, MS
The results were somewhat surprising. Working at a cancer center, we always think we are seeing a specialized population of younger patients with cancer seeking care at City of Hope. However, this data suggests that younger cancer incidence is growing across the spectrum of multiple cancers. This data speaks to efforts in early detection and then survivorship. We need to focus on two areas of the spectrum — screening and survival. These efforts could increase the chances that we will treat patients early — potentially curing them. This generation has had unique changes to their diets and behaviors compared with the generation before them. Many risk factors are known, and the onus is placed on the individual to prevent them. Examples of lifestyle choices that could decrease cancer risk include eating less processed foods, mitigating obesity and increasing physical activity.
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