Even though cancer rates continue to fall in older populations, the disease is becoming ever more common among younger age groups. A recent analysis of data from 13 cancer registries in the United States published by Rosenberg et al in JAMA Network Open found that those born between 1965 and 1980 (also known as Generation X) might have higher incidence rates of some malignancies, including thyroid, colorectal, kidney, and uterine corpus cancers, as well as leukemia.
Now, a large study led by researchers at the American Cancer Society investigating trends in cancer incidence and mortality by birth cohort has found that 17 of 34 cancers are increasing in Generation X and Millennials (those born between 1981 and 1996) compared to older generations. Mortality rates are also on the rise in younger adults. These findings, published by Hyuna Sung, PhD, and colleagues in The Lancet Public Health, highlight the need to identify and tackle underlying risk factors to inform prevention strategies, said the study authors.
Hyuna Sung, PhD
Study Methodology
The researchers obtained incidence data from 23,654,000 patients diagnosed with 34 types of cancer and mortality data from 7,348,137 deaths from 25 types of cancer for individuals aged 25 to 84 years from January 1, 2000, to December 31, 2019, from the North American Association of Central Cancer Registries and the United States National Center for Health Statistics, respectively. They then calculated birth cohort–specific incidence rate ratios and mortality rate ratios, separated by 5-year intervals from 1920 to 1990, adjusting for age and period effects by nominal birth cohort.
Results
The researchers found that incidence rate ratios increased with each successive birth cohort born since approximately 1920 for 8 of 34 cancers (P cohort < .050). Notably, the incidence rate was approximately two to three times higher in the 1990 birth cohort than in the 1955 birth cohort for small-intestine (incidence rate ratio [IRR] = 3.56, 95% confidence interval [CI] = 2.96–4.27), kidney and renal pelvis (IRR = 2.92, 95% CI = 2.50–3.42), and pancreatic (IRR = 2.61, 95% CI = 2.22–3.07) cancers in both male and female individuals, and for liver and intrahepatic bile duct cancer in female individuals (IRR = 2.05, 95% CI = 1.23–3.44).
In addition, the incidence rate ratios increased in younger cohorts, after a decline in older birth cohorts, for nine of the remaining cancers (P < .050): estrogen receptor–positive breast cancer, uterine corpus cancer, colorectal cancer, non–cardia cohort gastric cancer, gallbladder and other biliary cancer, ovarian cancer, testicular cancer, anal cancer in male individuals, and Kaposi sarcoma in male individuals.
Across cancer types, the incidence rate in the 1990 birth cohort ranged from 12% (IRR 1990 vs 1975 1.12, 95% CI = 1.03–1.21 for ovarian cancer) to 169% (IRR 1990 vs 1930 2.69, 95% CI = 2.34–3.08 for uterine corpus cancer) higher than the rate in the birth cohort with the lowest incidence rate. The mortality rate ratios increased in successively younger birth cohorts alongside incidence rate ratios for liver and intrahepatic bile duct cancer in female individuals, and uterine corpus, gallbladder and other biliary, testicular, and colorectal cancers, while mortality rate ratios declined or stabilized in younger birth cohorts for most cancer types.
Without effective population-level interventions, and as the elevated risk in younger generations is carried over as individuals age, an overall increase in cancer burden could occur in the future, halting or reversing decades of progress against the disease.— Ahmedin Jemal, DVM, PhD
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“Seventeen of 34 cancers had an increasing incidence in younger birth cohorts, including 9 that previously had declining incidence in older birth cohorts. These findings add to growing evidence of increased cancer risk in younger generations, highlighting the need to identify and tackle underlying risk factors,” concluded the study authors.
Addressing Underlying Cancer Risk Factors in Younger Adults
“The increase in cancer rates among this younger group of people indicate generational shifts in cancer risk and often serve as an early indicator of future cancer burden in the country,” said Ahmedin Jemal, DVM, PhD, Senior Vice President, Surveillance and Health Equity Science at the American Cancer Society, and senior author of this study. “Without effective population-level interventions, and as the elevated risk in younger generations is carried over as individuals age, an overall increase in cancer burden could occur in the future, halting or reversing decades of progress against the disease. The data highlights the critical need to identify and address underlying risk factors in Gen X and Millennial populations to inform prevention strategies.”
Dr. Sung, of the American Cancer Society, is the corresponding author of The Lancet Public Health report.
Disclosure: Funding for this study was provided by the American Cancer Society. For full disclosures of the study authors, visit thelancet.com.
