Differences in cancer rates among adults born between 1920 and 1990 in the USA: an analysis of population-based cancer registry data.

Background: Trends in cancer incidence in recent birth cohorts largely reflect changes in exposures during early life and foreshadow the future disease burden. Herein, we examined cancer incidence and mortality trends, by birth cohort, for 34 types of cancer in the USA.

Methods: In this analysis, we obtained incidence data for 34 types of cancer and mortality data for 25 types of cancer for individuals aged 25-84 years for the period Jan 1, 2000, to Dec 31, 2019 from the North American Association of Central Cancer Registries and the US National Center for Health Statistics, respectively. We calculated birth cohort-specific incidence rate ratios (IRRs) and mortality rate ratios (MRRs), adjusted for age and period effects, by nominal birth cohort, separated by 5 year intervals, from 1920 to 1990.

Findings: We extracted data for 23 654 000 patients diagnosed with 34 types of cancer and 7 348 137 deaths from 25 cancers for the period Jan 1, 2000, to Dec 31, 2019. We found that IRRs increased with each successive birth cohort born since approximately 1920 for eight of 34 cancers (p_cohort<0·050). 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 (IRR 3·56 [95% CI 2·96-4·27]), kidney and renal pelvis (2·92 [2·50-3·42]), and pancreatic (2·61 [2·22-3·07]) cancers in both male and female individuals; and for liver and intrahepatic bile duct cancer in female individuals (2·05 [1·23-3·44]). Additionally, the IRRs increased in younger cohorts, after a decline in older birth cohorts, for nine of the remaining cancers (p_cohort<0·050): oestrogen-receptor-positive breast cancer, uterine corpus cancer, colorectal cancer, non-cardia 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 [2·34-3·08] for uterine corpus cancer) higher than the rate in the birth cohort with the lowest incidence rate. The MRRs increased in successively younger birth cohorts alongside IRRs for liver and intrahepatic bile duct cancer in female individuals, uterine corpus, gallbladder and other biliary, testicular, and colorectal cancers, while MRRs declined or stabilised in younger birth cohorts for most cancers types.

Interpretation: 17 of 34 cancers had an increasing incidence in younger birth cohorts, including nine 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.

Funding: American Cancer Society.