Abstract 7414: Fraction of cancers attributable to and prevented by modifiable reproductive factors and hormone use in 2020 in Korea

Abstract Backgrounds: Cancer is a significant health concern for women globally, with reproductive factors playing a key role in its incidence. The combined estrogen-progesterone oral contraceptives (COC) and hormone replacement therapy (HRT) have been identified as carcinogenic agents by the International Agency for Research on Cancer (IARC) with sufficient evidence in human. Additionally, no breastfeeding has been linked to cancer risk among women with experience of pregnancy, according to the World Cancer Research Fund (WCRF). In 2009, National Cancer Center Korea estimated the population attributable fraction (PAF) of cancer incidence attributable to these factors. As of 2024, updated data is necessary to assess PAF. Methods: Cancer sites and modifiable reproductive factors for PAF estimation were selected according to WCRF and IARC list of classifications with sufficient evidence in humans. Data on exposure prevalence was obtained from the Korea National Health and Nutrition Examination Survey (KNHANES) in 2005, assuming 15 years of latency from the risk exposure to the cancer incidence. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using KNHANES, Korean Genome and Epidemiology Study (KoGES), and National Health Examinees data from the National Health Insurance Services (NHIS) linked with Korea Central Cancer Registry. Cox proportional hazards models were used to estimate HRs, while adjusted by age groups, alcohol consumption, tobacco use, and body mass index. Pooled HRs with 95% CIs were estimated by a meta-analysis with random-effects models. PAF was calculated by Levin’s formula which includes exposure prevalence and HR. Results: In our study, the total PAF of cancer incidence due to modifiable reproductive factors and hormone use was 0.97% (1135 cases of cancer) in 2020. No breastfeeding attributed to 3.57% of breast cancer (671 cases) and 4.08% of ovarian cancer (90 cases). COC was responsible for 0.77% of breast cancer in women (190 cases) but also prevented 1.34 % of endometrium (47 cases), and 2.27 % of ovarian cancer (66 cases). HRT accounted for 0.61 % (59 cases) and 0.9% (12 cases) of breast and endometrium cancer, respectively. Conclusion: This study suggests that hormone use and modifiable reproductive factors attributed to cancer incidence up to 0.97% in Korea. Citation Format: Thoa Thi Vu, Yoon-Jung Choi, Su Jung Byoun, Ye Lin Min, Sue Kyung Park, Kwang Pil Koh, So-Seul Sung, Hae Dong Woo, Kyu-Won Jung, Ehwa Yun, Byungmi Kim, Jin Kyoung Oh, Yoonjoo Choi, Bohyun Park, Hong Gwan Seo, Boyoung Park, Jeong-Soo Im. Fraction of cancers attributable to and prevented by modifiable reproductive factors and hormone use in 2020 in Korea [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 7414.