Breast and thyroid cancers have imposed a significant burden to women's health worldwide. According to the latest cancer statistics in Korea, thyroid cancer is the most commonly diagnosed cancer among Korean women, followed by breast cancer, and both are accounting for 67.9% of new cases. A number of studies have established effectiveness of early detection with mammography. However, there is no proven method for effective secondary prevention for thyroid cancer. In 2002, Korea began a nationwide breast cancer screening service as a part of the National Cancer Screening Program (NCSP) to provide mammography for women aged 40 years or over, in the price of free or 10% copayment. Thyroid cancer is not included in the NCSP, and the Korean national cancer screening guidelines specify the insufficient evidence in performing thyroid cancer screening among asymptomatic persons. However, providers frequently offer opportunistic screening with ultrasonography as an add-on for other cancer screening services. The current study aimed to assess the latest screening utilization, and to examine socioeconomic inequalities in breast and thyroid cancer screening in 2016. Subgroup analyses were conducted to explore the effect of inequalities according to age groups.

Data from the 2016 Korean Study of Women's Health Issues (K-Stori), a nationwide cross-sectional survey, were utilized. A total of 6500 women aged 40–79 were included for analysis. Screening status was defined as ‘screened’ for women who underwent mammography or ultrasonography within 2 years for breast and thyroid cancer, respectively. Absolute and relative inequalities in breast and thyroid cancer screening rates by socioeconomic factors (household income, education, urbanization, health literacy and social support) were estimated by inequality-specialized and regression-based indicators, Slope Index of Inequality (SII) and Relative Index of Inequality (RII).

A total of 70.1% and 50.6% of Korean women were shown to undergo in breast and thyroid cancer screening, respectively. The SII, an absolute inequality, and RII, a relative inequality, indicated substantial socioeconomic inequalities in 2016. Korean women with higher social supports were significantly more likely to undergo breast cancer screening [SII: 15.1 (95% CI: 11.1 to 19.1), RII: 2.2 (95% CI: 1.8 to 2.6)]. Inequalities in mammographic screening by health literacy levels were also significant, favored women with higher literacy [SII: 10.2 (95% CI: 6.2 to14.3), RII: 1.7 (95% CI: 1.4 to 2.1)]. In contrast, women living in the metropolitan area were less likely to undergo in breast cancer screening [SII: −9.4 (95% CI: −13.5 to −5.3), RII: 0.6 (95% CI: 0.5 to 0.7)]. Inequalities by education or household income were not observed for breast cancer screening. Socioeconomic inequalities in thyroid cancer screening were similar to those found in breast cancers screening, except household income levels. Inequalities by income levels were observed significant only in thyroid cancer screening, favored women in higher income levels [SII: 10.2 (95% CI: 5.4 to 15.0), RII: 1.5 (95% CI: 1.2 to 1.8)].

The patterns of inequalities were also differed by subgroup analyses according to age groups. Women aged 40–49 showed inequalities by household income levels for both breast and thyroid cancer screening. For women aged 50s, income inequalities were found only for thyroid cancer screening, but not breast cancer. Socioeconomic factors of social support and health literacy were significant among older women aged 60-79, favored women in higher support and literacy in both cancer screening.

Different socioeconomic inequalities were found according to age groups in Korean women, which should be approached by specialized policies. More importantly, thyroid cancer screening is not currently recommended, and has intensified socioeconomic inequalities among Korean women.