Abstract 128: Chronological changes of hormone receptor status in breast cancer by reproductive factors: results from Seoul Breast Cancer Study (SeBCS).
Authors: Chung Seokang , Song Nan , Sung Hyuna , Park Sue K. , Han Wonshik , Noh Dong-Young , Ahn Sei-Hyun , Yoo Keun-Young , Kang Daehee , Choi Ji-Yeob 
Published: August 2014

Abstract
Lifestyle factors have been chronologically changed into western-style in Korea, which may result in the rapid increase of breast cancer incidence. It is plausible reproductive factors through hormonal mechanisms are differentially related to risk of breast cancer subtypes defined estrogen receptor (ER) and progesterone receptor (PR) status. We investigated the differential association of reproductive risk factors on such subtypes and also evaluated the temporal trends between those factors and the subtypes.
Using data of Seoul Breast Cancer Study (SeBCS), a multicenter based case-control study, 3,689 breast cancer patients and 3,870 control subjects were analyzed in this study. The distribution of subtypes among cases was 62.7% of ER+, 37.3% ER-, 53.2% of PR+ and 46.8% PR-, respectively. Reproductive factors including age at menarche, pregnancy history, age at first full term pregnancy, number of children, duration of estrogen exposure before first full term pregnancy (EEBF), duration of lifetime estrogen exposure (LEED), breast feeding history and duration of breast feeding were evaluated on breast cancer risk by hormone receptor status. Multinomial logistic regression and Wald tests for heterogeneity across the subtypes were conducted.
The frequency of PR-positive breast cancer significantly was higher among the women born in 1960s (56.4%) compared to women born in 1940s (41.9%) (p for trend &lt;0.0001). However, there was no significant trend of the distribution in ER-defined breast cancer subtype. Breast cancer risks associated with number of children, EEBF, LEED, duration of breast feeding were different between ER or PR status (all p for heterogeneity &lt;0.05). Those reproductive factors showed a chronological trend according to the birth year groups. EEBF was longer among the women born in 1960s group than women born in 1940s. As the EEBF increased, the risk of breast cancer increased significantly; this association was stronger among PR-positive (OR= 1.96, 95% CI= 1.65 - 2.33 for Q4 vs Q1) than among PR-negative cancer (OR= 1.48, 95% CI= 1.24 - 1.77 for Q4 vs Q1) (p for heterogeneity= 0.0100). LEED was shorter among the women born in 1960s group than women born in 1940s. As the LEED increased, the risk of breast cancer decreased significantly, which is stronger among PR-negative (OR= 0.67, 95% CI= 0.57 - 0.79 for Q4 vs Q1) than among PR-positive cancer (OR= 0.89, 95% CI= 0.76 - 1.05 for Q4 vs Q1) (p for heterogeneity= 0.0014).
Our results suggest that association between the reproductive risk factors and breast cancer risk differs appreciably for breast cancer defined by hormone receptor status. Increasing distribution of PR-positive breast cancer might be attributed to changes of EEBF and LEED.
Citation Format: Seokang Chung, Nan Song, Hyuna Sung, Sue K. Park, Wonshik Han, Dong-Young Noh, Sei-Hyun Ahn, Keun-Young Yoo, Daehee Kang, Ji-Yeob Choi. Chronological changes of hormone receptor status in breast cancer by reproductive factors: results from Seoul Breast Cancer Study (SeBCS). [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 128. doi:10.1158/1538-7445.AM2013-128