Cancer incidence rates significantly increased among younger U.S. adults, with some types showing up to a threefold rise in the 1990 birth cohort compared to earlier generations. The increase may outweigh improvements in cancer survival, noted investigators.
Hyuna Sung, PhD, and colleagues from the American Cancer Society conducted a comprehensive analysis of population-based cancer registry data to examine trends in cancer incidence and mortality among various birth cohorts in the U.S.
The study, published in The Lancet Public Health, analyzed data for 34 cancer types diagnosed in individuals aged 25 to 84 years from January 1, 2000, to December 31, 2019. Incidence data were sourced from the North American Association of Central Cancer Registries, while mortality data were obtained from the U.S. National Center for Health Statistics. The study analyzed data from 23,654,000 patients diagnosed with 34 cancer types and 7,348,137 deaths from 25 cancer types between January 1, 2000, and December 31, 2019.
Incidence rates for 17 of the 34 cancer types increased in successively younger birth cohorts, particularly those born after 1920. Notable increases were observed for cancers of the small intestine, kidney and renal pelvis, pancreas, and liver and intrahepatic bile duct in females.
The 1990 birth cohort had incidence rates 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 that were approximately two to three times higher compared to the 1955 birth cohort for both males and females. Additionally, females in the 1990 cohort had more than double the incidence rate for liver and intrahepatic bile duct cancer (IRR 2.05 [95% CI 1.23–3.44]). In the 1990 birth cohort, cancer incidence rates were between 12% higher for ovarian cancer (IRR 1.12 [95% CI 1.03–1.21]) and 169% higher for uterine corpus cancer (IRR 2.69 [95% CI 2.34–3.08]) compared to the cohort with the lowest recorded rates.
Incidence rates for liver and non-HPV-associated oral and pharyngeal cancers rose in women born around 1970, while rates either decreased or remained stable in men.
For young adults aged 25 to 49 years, the highest annual increases in cancer incidence rates were observed for pancreatic cancer (4.34% in ages 25–29 years), small intestine cancer (4.22% in ages 25–29 years), and kidney and renal pelvis cancer (3.93% in ages 35–39 years).
After declining in older birth cohorts, the IRRs increased in younger cohorts for nine other cancers: estrogen-receptor-positive breast cancer, uterine corpus cancer, colorectal cancer, non-cardia gastric cancer, gallbladder and other biliary cancers, ovarian cancer, testicular cancer, anal cancer in males, and Kaposi sarcoma in males.
Mortality trends generally paralleled incidence trends for several cancers, including liver, uterine corpus, gallbladder, testicular, and colorectal.
The study also found that incidence rates for 14 out of the 34 cancer types decreased or remained relatively stable across successive birth cohorts from approximately 1955 to 1990.
The obesity epidemic in the U.S. since the late 1970s might have played a role in the emerging cancer trends among younger generations, as 10 out of the 17 cancers with increasing incidence rates were obesity related.
Researchers highlighted the need for further research to identify the underlying risk factors responsible and to develop targeted prevention strategies and interventions that align with the social and cultural context, values, and preferences of younger generations.
They acknowledged limitations of the study, such as the inherent issues with age-period-cohort modeling, the inability to assess the contribution of changes in risk factors or diagnostic practices due to the lack of data, and the potential misclassification of certain cancers.
This study was funded by the American Cancer Society; the authors declared no competing interests.
