Breast Cancer Research and Treatment 80: 127–131, 2003. © 2003 Kluwer Academic Publishers. Printed in the Netherlands. Brief communication Estrogen receptor alpha gene polymorphisms and breast cancer risk Aesun Shin 1 , Daehee Kang 1 , Hisahide Nishio 2 , Myeong Jin Lee 2 , Sue Kyung Park 3 , Sook-Un Kim 1 , Dong-Young Noh 4 , Kuk-Jin Choe 4 , Se-Hyun Ahn 5 , Ari Hirvonen 6 , Ju Han Kim 1 , and Keun-Young Yoo 1 1 Department of Preventive Medicine, Seoul National University College of Medicine, Seoul, South Korea; 2 Division of Public Health, Kobe University Graduate School of Medicine, Kobe, Japan; 3 Department of Preventive Medicine, Konkuk University College of Medicine, Chungcheongbuk-do; 4 Department of Surgery, Seoul National University College of Medicine, Seoul; 5 Department of Surgery, Ulsan University College of Medicine, Seoul, South Korea; 6 Department of Industrial Hygiene and Toxicology, Finnish Institute of Occupational Health, Helsinki, Finland Key words: breast cancer, estrogen receptors, polymorphism (genetics) Summary We conducted a hospital-based case-control study to evaluate the association between the XbaI and PvuII restriction fragment length polymorphisms (RFLPs) in intron 1 of the estrogen receptor α (ERα) gene and breast cancer risk. The study population consisted of 205 histologically confirmed incident breast cancer cases and 205 age-matched controls with no present and previous history of cancer. The PvuII genotype distribution did not show any difference between cases and controls, but the adjusted odds ratio (OR) for the XbaI X allele containing genotypes was 0.4 (95% CI: 0.3–0.6) compared with the xx genotype. The decrease in the OR appeared to be more attributable to the postmenopausal women; the ORs were 0.3 (95% CI: 0.1–0.5) and 0.5 (95% CI: 0.3–0.9) for postmenopausal and premenopausal women, respectively. Our results therefore suggest that the ERα XbaI polymorphism modifies individual susceptibility to breast cancer in Korean women. Introduction Breast cancer is the second most frequent cancer in Korean women and the incidence is increasing [1]. Fa- milial history of breast cancer and reproductive factors are well-established risk factors of breast cancer. How- ever, genetic polymorphisms of genes involved in metabolism of hormones or other carcinogens are evolving as important determinants of breast cancer susceptibility [2]. The estrogen receptor α (ERα) is an import- ant mediator of the hormonal response in estrogen- sensitive tissues such as breast, endometrium, and bone. In agreement with this, potentially import- ant polymorphisms in the ERα gene have, although inconsistently, been associated with bone density [3] and breast cancer [4–7] and endometrial cancer risks [8]. Most of these studies on ERα gene polymor- phisms and breast cancer were conducted in western countries. Since oriental women may have different genotype distribution or different level of suscepti- bility compared with western women, we conducted a hospital-based case-control study to examine this issue further by evaluating the potential association between the genetic polymorphism of intron 1 (PvuII and XbaI) of ERα gene and breast cancer risk in Korean women. Materials and methods The study population was selected from three teaching hospitals located in Seoul, South Korea (Seoul Na- tional University Hospital, Borame Hospital and Asan Medical Center) between March 1994 and December