The incidence of breast cancer has recently been ranked first in Korea. This is a population-based cohort study that aims to evaluate the risk of breast cancer from the use of hormone replacement therapy (HRT). A total of 9579 participants were observed between January 1998 and June 2004; 6108 women who took HRT constituted the HRT group, and 3471 women who did not take HRT constituted the non-HRT group. Using the database from the Korea Central Cancer Registry, the authors examined the incidence of breast cancer from HRT. A total of 26 cases of breast cancer developed in the HRT group as compared with the 13 cases in the non-HRT group, during the follow-up period. The relative risk of developing breast cancer in the HRT group was 1.16 times higher than in the non-HRT group, with a population attributable risk of 29.9%. The risk of breast cancer in the HRT group increased when the risk factors were adjusted in the model.
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