Abstract C106: Income inequality and its influence on cancer mortality: A 20-year longitudinal study across 73 countries

Abstract Background: Income inequality is a key structural determinant of cancer mortality, associated with disparities in access to timely treatment and follow-up care. However, its long-term impact on cancer mortality, including the lagged (or delayed) effects, remains understudied in cross-national research. This study examined lagged effects of income inequality on cancer mortality across 73 countries over 20 years to inform global cancer control strategies. Methods: We analyzed data from 73 countries (2000–2019) with complete data on income inequality and cancer mortality, using inequality data from the Standardized World Income Inequality Database and mortality data from the WHO. Annual income inequality was assessed using the Gini coefficient, quantifying income distribution within a country, with higher values for greater inequality. Annual age-standardized mortality rates (per 100,000) were obtained for overall and 25 site-specific cancers. Cancer sites were categorized into survival groups based on mortality-to-incidence ratios from GLOBOCAN: <0.3 (high), 0.3-0.6 (medium), and >0.6 (low). Covariates included the age-dependency ratio (ratio of 0-14 and 65+ to 15-64) from the World Bank and health system indicators (i.e., healthcare expenditure per capita, physician density) from the WHO. All continuous variables, including the Gini coefficient and health system indicators, were standardized as z-scores. We used Generalized Estimating Equations with an exchangeable correlation structure to account for repeated measures within countries and fitted separate models for each lag year (0-10) to identify when the association between income inequality and mortality emerges and reaches its peak. Results: A one-standard deviation increase in the Gini coefficient was not significantly associated with higher overall cancer mortality during the first 3 lag years (p-values>0.05). However, the association became significant at a 4-year lag (β=8.75, 95% confidence interval [CI]=1.05-16.46) and peaked at an 8-year lag (β=11.60, 95% CI=2.10-21.11), corresponding to an increase of 9 to 12 cancer deaths per 100,000 population. For low-survival cancers, significant associations were found from a 0-year lag (β=3.92, 95% CI=0.71-7.13), peaking at an 8-year lag (β=7.13, 95% CI=3.09-11.16). Among individual cancers, lung cancer had a significant association from a 0-year lag (β=2.40, 95% CI=0.28-4.53), peaking at a 5-year lag (β=3.30, 95% CI=1.17-5.44). Similarly, stomach cancer was associated with income inequality at a 0-year lag (β=2.52, 95% CI=0.92-4.13), with the peak effect at a 5-year lag (β=2.91, 95% CI=1.57-4.25). No significant associations were found for medium- or high-survival cancers. Conclusion: Income inequality demonstrates a lagged association with cancer mortality, particularly for low-survival cancers, underscoring the importance of accounting for the delayed effects of social and economic conditions on health outcomes over time. National policies targeting structural disparities are critical to improving long-term cancer outcomes worldwide. Citation Format: Jaesung Choi, Mary G. Nusloch, Nickhill Bhakta, Kirsten K. Ness, Melissa M. Hudson, Gregory T. Armstrong, Yutaka Yasui, I-Chan Huang. Income inequality and its influence on cancer mortality: A 20-year longitudinal study across 73 countries [abstract]. In: Proceedings of the 18th AACR Conference on the Science of Cancer Health Disparities; 2025 Sep 18-21; Baltimore, MD. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2025;34(9 Suppl):Abstract nr C106.