Abstract C72: Changing patterns of socioeconomic inequalities in women cancer screening in South Korea with ten years follow-up of nationwide cross-sectional study
Authors: Choi Eunji , Lee Yoon Young , Suh Mina , Park Boyoung , Jun Jae Kwan , Kim Yeol , Choi Kui Son 
Published: February 2019

Purposes: Encouraging screening participation for breast and cervical cancer is essential for effective cancer control. Republic of Korea introduced National Cancer Screening Program in 2002, covering all Korean residents living within the country. In the program, mammography and Pap test have been provided biannually for all Korean women for free or 10% of copayment of original cost by income levels. Individuals can have opportunistic cancer screening by their own requests, but they must pay for all procedure-related costs.

It is worthy of note that the screening rate compliant with recommendation guideline for breast and cervical cancer has risen from 2004 onward. For breast cancer screening, the rate increased from 33.2% in 2004 to 59.7% in 2013 with the annual percent change of 3.7%. Furthermore, cervical cancer screening participation annually escalated during 2004 (58.3%) and 2013 (67.0%). However, these gains may not be equally distributed across socioeconomic status.

The current study aimed to examine socioeconomic inequalities in organized and opportunistic cancer screening of breast and cervical cancer from 2005 to 2015. The corresponding result would be greatly influential to identify particular groups that may be experiencing a high burden of cancer, and to succeed long-term consequences of screening program.

Methods: Summarized data for the analysis were obtained from Korean National Cancer Screening Survey (KNCSS) from 2005 to 2015 in every other year. The KNCSS is a nationwide and population-based cross-sectional survey performed annually to investigate cancer screening-related behaviors for five major cancers (i.e., stomach, liver, colorectal, breast, and cervix uteri).

Survey samples were selected by using a stratified, multistage, and random sampling procedure according to geographic area, size of population per area, and age of Korean population. According to the protocols of the NCSP, people older than 40 years of age are eligible to undergo breast cancer screening; and women older than 30 years of age are eligible to undergo cervical cancer screening.

From 2005 to 2015, the data were collected through face-to-face interviews by a professional research agency. Informed consent was obtained from all study participants. Using a structured questionnaire, participants were asked about their experience with screening for five cancer types (i.e., stomach, liver, colorectal, breast and cervix uteri), and sociodemographic characteristics, including income level. The questions included “Have you ever undergone [cancer type] screening?” and “Which screening method have you experienced?” For the interval between screenings, the question was as follows: “When did you last undergo [cancer type] screening with this method?”

A total of 7,939 women aged 40-74 and 10,659 women aged 30-39 were included for the analysis of breast and cervical cancer screening, respectively. Screening rates were calculated from 2005 to 2015. Screening rate for breast cancer was defined as percentage of women with 40 years of age or older who had last undergone screening with mammography within a period of 2 years; that of cervical cancer as percentage of women 30 years of age or older who had last undergone screening with conventional cytology within a period of 2 years. The screening rates of breast and cervical cancer were depicted for the baseline characteristics of the study population. The average annual percent change (APC) during 2005 and 2015 was further estimated in each breast and cervical screening rate.

Absolute and relative indices of inequality were used to present differences in screening rates by socioeconomic status (SES). Slope Index of Inequality (SII) is interpreted as absolute difference of inequality between the most privileged group and the least privileged, while Relative Index of Inequality is a ratio of the two groups. Thus, production of both measures (SII and RII) is required to delineate a complete picture of inequalities. Because the data were obtained in summarized table, we calculated all measures through Microsoft Excel.

Results: Total screening rate in breast cancer had gradually increased from 39.1% to 61.3% during 2005 to 2015 from KNCSS data [2005 (39.1); 2007 (45.8); 2009 (55.2); 2011 (60.5); 2013 (59.7); 2015 (61.3)]. The APC on average of total study population was 4.4% during ten years. Women who had elementary (2.7%) or middle schooling (2.5%), or were without formal schooling (2.4%) showed lower APC, compared to the average APC. Women with the lowest household income status rated 1.2% of APC, much lower than average of it. The screening rates of all socioeconomic groups (age, household income, and education level) had moved similar way to increase, while the gap between lowest and highest quintiles had been intensified. Women aged 50-69 and women in the highest quintile of household income and education were more likely to participate in breast cancer screening. The gaps in breast cancer screening in 2005 between the lowest and highest quintiles of income and education were only around 1.0% (40.9, 39.9) and 7.8% (41.1, 33.3), but increased to 22.7% (68.5, 45.8) and 17.75% (63.2, 45.5) in 2015.

Slightly different patterns were detected for cervical cancer. Screening rates for total had increased from 2005 (57.4%) to 2013 (67.01), while the rate fell short in 2015 [2005 (57.4); 2007 (57.1), 2009 (63.9), 2011 (62.4), 2013 (67.0), and 2015 (65.6)]. The APC during 2005 and 2015 was estimated to be 1.6%. The highest increase of APC was observed in women of elementary graduates (2.3%), though the screening rates were lower compared to other groups over all periods. Women who aged 40-49 showed a decreasing APC in participation rates between 2005 and 2015. In other words, the gap between the highest and lowest quintiles of household income and education level did not change a lot during 2005 to 2015, while the magnitudes of each gap were maintained to be very high around 15% and 35%, respectively, for household income and education. Women aged 50-69 who responded to the more than $4,000 in household income and completed college or more, were likely to undergo cervical screening in all periods.

Inequality indicators (SII and RII) showed changing patterns of socioeconomic inequalities in breast and cervical cancer screening participation. Because SII is obtained by the difference of screening participation rates from the most-privileged to the least-privileged group, it has both negative and positive values. RII is a measure of ratio from the most privileged divided by the least privileged group, having only positive values but no limit to the positive end.

In breast cancer screening, SII had negative values by age groups in all years [2005 (-53.0), 2007 (-37.3), 2009 (-38.5), 2011 (-38.4), 2013 (-41.8), 2015 (-37.4)], because the screening rate from the highest quintile of age (70-79) was lower than that of the lowest quintile of age (40-49). In line with the results, RII had values less than 1 years [2005 (0.13), 2007 (0.23), 2009 (0.22), 2011 (0.22), 2013 (0.18), 2015 (0.23)]. SII for education levels changed the most from negative to positive values during 2005 and 2015 [2005 (-1.5); 2007 (-3.8); 2009 (12.9); 2011 (26.2); 2013 (9.1); 2015 (35.1)], indicating that groups of lower quintiles in education had higher screening rates in early years, but it rapidly changed to opposite direction as it came to recent years. RII for education increased in succession 2015 [2005 (0.9), 2007 (0.8), 2009 (1.9), 2011 (3.5), 2013 (1.7), 2015 (4.9)].

In the setting of cervical cancer screening, age group produced negative SII for all years, just as we found in breast cancer. By education quintiles, SII seemed to increase continuously during 2005 and 2015 [2005 (26.6); 2007 (24.8); 2009 (29.7); 2011 (37.4); 2013 (41.6); 2015 (41.9)]. RII for education showed similar trend. By household income, SII was decreased from 2005 to 2009, while it started to increase from 2011 [2005 (12.5), 2007 (3.5), 2009 (0.6), 2011 (-2.7), 2013 (7.5), 2015 (13.2)]. RII also corresponded with the SII results.

Furthermore, we estimated trend lines by plotting SII as value of y-axis and years as x-axis. As years went on, education inequalities were intensified with linear coefficient of 3.4 and 1.9, respectively, for breast and cervical cancer screening participation. Income inequality for breast cancer seemed to decrease with -0.1 of coefficient of the linear trend, while it increased for cervical cancer screening rates with 0.2.

Conclusion: There is consistent evidence throughout the world that socially deprived people suffer a heavier burden of cancer with higher mortality rates. Breast cancer is the second most common cancer and the fifth leading cause of cancer death among Korean women. Cervical cancer incidence rate in South Korea is still higher than that of other developed countries.

Screening rates compliant with recommendation guideline have increased with recommendation in all SES from the introduction of National Cancer Screening Program onward. However, our data represented that the improvement of total participation rate was chiefly due to the large increase in women in higher levels of household income and education. In addition, the gap of screening participation seemed to decrease during 2005 and 2009, but started to widen again from 2011, especially for education level. Therefore, to decrease socioeconomic inequalities in cancer-screening participation of Korean women, a tailored approach should be given to promote health behaviors in cancer control by education level.

Citation Format: Eunji Choi, Yoon Young Lee, Mina Suh, Boyoung Park, Jae Kwan Jun, Yeol Kim, Kui Son Choi. Changing patterns of socioeconomic inequalities in women cancer screening in South Korea with ten years follow-up of nationwide cross-sectional study [abstract]. In: Proceedings of the Tenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2017 Sep 25-28; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2018;27(7 Suppl):Abstract nr C72.