Socioeconomic inequality in organized and opportunistic screening for breast cancer: results from the Korean National Cancer Screening Survey, 2009-2021.

Breast cancer screening rates have increased since the introduction of the National Cancer Screening Program (NCSP) in Korea. However, it remains unclear whether socioeconomic inequalities have improved, particularly according to screening type. This study investigated inequalities in organized (government-led) and opportunistic (individually initiated) screening, stratified by education and income levels. Data were obtained from the Korean National Cancer Screening Survey, conducted annually from 2009 to 2021, involving approximately 1,700 women each year except in 2009. Trends were analyzed using joinpoint regression to calculate average annual percent changes (AAPCs). Socioeconomic inequalities were assessed using the slope index of inequality (SII) and relative index of inequality (RII). Organized screening rates increased from 42.0% in 2009 to 60.2% in 2021 (AAPC, 1.9; 95% confidence interval [CI], 0.7-3.4), whereas opportunistic screening rates declined from 13.3% to 11.2% (AAPC, -5.4; 95% CI, -8.7 to -2.3). For organized screening, individuals with lower education levels exhibited higher participation, resulting in negative inequality indices (SII, -5.37%; RII, 0.80). No significant income-based inequality was found (SII, 1.60; RII, 1.07). However, opportunistic screening demonstrated significant inequalities by both education (SII, 5.37%; RII, 1.92) and income (SII, 5.90%; RII, 1.96), with higher participation rates among more advantaged groups. The NCSP has improved breast cancer screening rates and reduced income-related inequality in organized screening. However, educational and income-based inequalities persist in opportunistic screening. To reduce screening inequities, policy efforts are needed to further promote the NCSP, including improving program quality and providing financial support for follow-up examinations.