Postmenopausal hormone therapy and cancer risk P. Kenemans * , R.A. Verstraeten, R.H.M. Verheijen Department of Obstetrics and Gynaecology, VU University Medical Center, P.O. Box 7057, 1007 MB Amsterdam, The Netherlands Abstract. Postmenopausal Hormone Replacement Therapy has been implicated in the develop- ment of four frequent female tumors: endometrial cancer, breast cancer, ovarian cancer and colorectal cancer. Estrogens are only weak genotoxic, mutagenic carcinogens, but could induce tumors by way of accumulation of incessant DNA replication damage. While estrogen (only) hormone replacement therapy (ERT) increases the risk of endometrial carcinoma and probably of ovarian carcinoma, ERT seems to be neutral for the breast and colorectal cancer. With combined estrogen progestagen replacement therapy (HRT), there is no increased risk of endometrial cancer nor of ovarian cancer. The risk of breast cancer, however, is slightly increased with long-term use. Colorectal cancer risk is probably reduced with combined HRT use. Data are only available for oral use; for transdermal, intranasal and other use no data are available. D 2005 Elsevier B.V. All rights reserved. Keywords: Estrogens; Progestagens; HRT; Cancer risk; Breast cancer 1. Introduction In postmenopausal women the risk of cancer increases with age [1]. Breast cancer is the most common malignancy in women. Worldwide, endometrial carcinoma is the second most common gynecological cancer after breast carcinoma, while ovarian cancer is the main cause of death among the gynecological malignancies. Colorectal cancer is the most frequent neoplasm among non-smoking women in the Western world, and in the United States it is the third highest cause of death after lung and breast cancers, respectively. 0531-5131/ D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.ics.2005.01.004 * Corresponding author. E-mail address: Kenemans@vumc.nl (P. Kenemans). International Congress Series 1279 (2005) 133 – 140 www.ics-elsevier.com