Income Disparity in Breast Cancer Incidence and Stage at Presentation: A National Population Study of South Korea.

Purpose: This study aims to explore income-based disparities in breast cancer (BC) incidence and stage at presentation in a national population in South Korea, where a National Cancer Screening Program (NCSP) has been implemented.

Methods: In 2007, new patients with BC were identified using the Korea Central Cancer Registry database. We calculated adjusted odds ratios (aORs) to evaluate the association between individual income level and the risk of distant stage BC at presentation, adjusting for women's age, body mass index, disability registration, employment, region of residence, and year of diagnosis.

Results: The cumulative age-standardized incidence of BC in the 11 years was highest among women in the richest quintile (2,040 per 100,000 women for 11 years), whereas the proportion of distant stage at presentation was the highest (10.2%) among the medical aid beneficiaries. The aOR of distant stage diagnosis at presentation was higher for lower-income quintiles, and the risk was the highest in the medical aid beneficiaries (aOR, 2.25; 95% confidence interval, 1.97-2.58) than in the richest quintile. The income-based gradient in aORs for distant stage did not differ between younger (< 40 years) and older patients.

Conclusion: A higher risk of distant stage BC at presentation among the lower-income and medical aid groups in the context of a NCSP was observed. A more focused approach toward women in lower-income groups is necessary to alleviate the disparity in the risk of advanced BC.