Persistent income-related inequalities in cancer screening utilisation in South Korea: Evidence from repeated cross-sectional data, 2013–2023

OBJECTIVE: This study aimed to examine trends in income-related inequalities in cancer screening from 2013 to 2023 and decompose these inequalities into contributing factors. STUDY DESIGN: This is a repeated cross-sectional study. METHODS: Data were drawn from the 2013, 2018, and 2023 waves of the nationally representative cross-sectional Korea National Health and Nutrition Examination Survey. Screening uptake was defined as having received any cancer screening within the past two years, reflecting Korea's biennial check-up schedule. Income-related inequality was assessed using the Erreygers concentration index (ECI) and the horizontal inequity index (HIwv). The ECI was decomposed to identify contributing factors. RESULTS: Screening rates increased across all income groups, with overall participation rising from 63.7 % in 2013 to 71.8 % in 2023. However, a widening pro-rich inequality was observed over this period. The ECI rose from 0.127 (standard error [SE]: 0.018) in 2013 to 0.149 (SE: 0.016) in 2023, and the HIwv increased from 0.108 (SE: 0.019) to 0.146 (SE: 0.016). Income and private health insurance (PHI) made the largest contributions. Income's share of inequality nearly doubled from 38.2 % to 71.4 %, while PHI's declined from 35.8 % to 24.9 %. CONCLUSIONS: Despite near-universal financial coverage, persistent pro-rich inequalities in cancer screening suggest that eliminating direct screening costs alone is insufficient to achieve equity. Broader strategies addressing structural and social barriers - including post-diagnosis financial concerns, time constraints, and gaps in education and health literacy - are required to ensure equitable access to preventive care.