Cancer Incidence Trends in Successive Social Generations in the US

Abstract

Importance: The incidence of some cancers in the US is increasing in younger age groups, but underlying trends in cancer patterns by birth year remain unclear.

Objective: To estimate cancer incidence trends in successive social generations.

Design, setting, and participants: In this cohort study, incident invasive cancers were ascertained from the Surveillance, Epidemiology, and End Results (SEER) program's 13-registry database (November 2020 submission, accessed August 14, 2023). Invasive cancers diagnosed at ages 35 to 84 years during 1992 to 2018 within 152 strata were defined by cancer site, sex, and race and ethnicity.

Exposure: Invasive cancer.

Main outcome and measures: Stratum-specific semiparametric age-period-cohort (SAGE) models were fitted and incidence per 100 000 person-years at the reference age of 60 years was calculated for single-year birth cohorts from 1908 through 1983 (fitted cohort patterns [FCPs]). The FCPs and FCP incidence rate ratios (IRRs) were compared by site for Generation X (born between 1965 and 1980) and Baby Boomers (born between 1946 and 1964).

Results: A total of 3.8 million individuals with invasive cancer (51.0% male; 8.6% Asian or Pacific Islander, 9.5% Hispanic, 10.4% non-Hispanic Black, and 71.5% non-Hispanic White) were included in the analysis. In Generation X vs Baby Boomers, FCP IRRs among women increased significantly for thyroid (2.76; 95% CI, 2.41-3.15), kidney (1.99; 95% CI, 1.70-2.32), rectal (1.84; 95% CI, 1.52-2.22), corpus uterine (1.75; 95% CI, 1.40-2.18), colon (1.56; 95% CI, 1.27-1.92), and pancreatic (1.39; 95% CI, 1.07-1.80) cancers; non-Hodgkins lymphoma (1.40; 95% CI, 1.08-1.82); and leukemia (1.27; 95% CI, 1.03-1.58). Among men, IRRs increased for thyroid (2.16; 95% CI, 1.87-2.50), kidney (2.14; 95% CI, 1.86-2.46), rectal (1.80; 95% CI, 1.52-2.12), colon (1.60; 95% CI, 1.32-1.94), and prostate (1.25; 95% CI, 1.03-1.52) cancers and leukemia (1.34; 95% CI, 1.08-1.66). Lung (IRR, 0.60; 95% CI, 0.50-0.72) and cervical (IRR, 0.71; 95% CI, 0.57-0.89) cancer incidence decreased among women, and lung (IRR, 0.51; 95% CI, 0.43-0.60), liver (IRR, 0.76; 95% CI, 0.63-0.91), and gallbladder (IRR, 0.85; 95% CI, 0.72-1.00) cancer and non-Hodgkins lymphoma (IRR, 0.75; 95% CI, 0.61-0.93) incidence decreased among men. For all cancers combined, FCPs were higher in Generation X than for Baby Boomers because gaining cancers numerically overtook falling cancers in all groups except Asian or Pacific Islander men.

Conclusions and relevance: In this model-based cohort analysis of incident invasive cancer in the general population, decreases in lung and cervical cancers in Generation X may be offset by gains at other sites. Generation X may be experiencing larger per-capita increases in the incidence of leading cancers than any prior generation born in 1908 through 1964. On current trajectories, cancer incidence could remain high for decades.

Figure 1.. Fitted Cohort Patterns by Cancer Site and Race and Ethnicity: Females

Estimated incidence per 100 000 person-years at age 60 years is shown by birth year (1908-1983). All curves are on the log₁₀ scale. These and additional curves are shown in eFigure 11 in Supplement 1. Tick marks on the x-axis indicate start years for consecutive social generations: 1928-1945, Silent Generation; 1946-1964, Baby Boomers; 1965-1980, Generation X. Shaded areas indicate 95% CIs.

Figure 2.. Fitted Cohort Patterns by Cancer Site and Race and Ethnicity: Males

Estimated incidence per 100 000 person-years at age 60 years is shown by birth year (1908-1983). All curves are on the log₁₀ scale. These and additional curves are shown in eFigure 13 in Supplement 1. Tick marks on the x-axis indicate start years for consecutive social generations: 1928-1945, Silent Generation; 1946-1964, Baby Boomers; 1965-1980, Generation X. Shaded areas indicate 95% CIs.

Figure 3.. Fitted Cohort Patterns for Leading Cancers Combined

Gen X indicates Generation X. Shaded areas indicate 95% CIs.

Figure 4.. Incidence by Cancer Site in Successive Generations

Fitted cohort pattern curves by cancer site are adjusted for race and ethnicity as described in the Methods, plotted on a natural log scale, and sorted from largest (top) to smallest (bottom). IRR indicates incidence rate ratio; NHL, non-Hodgkins lymphoma.

Figure 5.. Changes in Leading Cancer Incidence at Age 60 Years per 100 000 Person-Years in Successive Generations and Proxy Parents by Sex and Race and Ethnicity

Arrow plots indicate magnitude and direction of change from older to younger generations. Corresponding percentage changes and 95% CIs are also graphed in eFigure 19 in Supplement 1.