Increasing Incidence of Gallbladder Cancer among Non-Hispanic Blacks in the United States: A Birth Cohort Phenomenon

Background: Gallbladder cancer incidence varies among racial/ethnic subgroups in the United States (US). We investigated trends in gallbladder cancer incidence rates in 50 states from 2001 to 2018. Methods: Age-adjusted incidence rates and trends in adults were calculated using data from the US Cancer Statistics registry. We used joinpoint regression to compute annual percentage of changes (APC). We analyzed incidence trends by time periods, age groups, and birth cohorts through age–period-cohort modeling. Results: Overall, age standardized incidence rates for gallbladder cancer decreased by 0.3% annually between 2001 and 2018 [95% confidence interval (CI) −0.5% to −0.1%]. However, secular trends varied by race/ethnicity. Although gallbladder cancer rates declined in other racial/ethnic groups, rates increased by 1.4% annually among non-Hispanic Blacks (NHB) between 2001 and 2018 (APC = 1.4%; 95% CI, 0.9%–2.0%). We found evidence for period and birth cohort effects with increasing rates among successive birth cohorts of NHBs. Relative to NHB cohorts born circa 1946, gallbladder cancer rates were 85% higher in NHB cohorts born circa 1971 [incidence rate ratio (IRR), 1.85; 95% CI, 1.26–2.72). The rates among NHBs in South region were higher in cohorts born circa 1971 (IRR, 2.17; 95% CI, 1.27–3.73) relative to those born circa 1946. Conclusions: The incidence of gallbladder cancer has consistently increased in the US among NHBs. A notable increase in incidence was observed among NHBs with evidence of birth cohort effects in South, Northeast, and Midwest regions. Impact: The cohort effect observed among NHBs with increasing rates in different US regions suggests that gallbladder cancer rates will continue to rise in the US in the near future.