Hormone replacement therapy and risk of epithelial ovarian cancer

It has been suggested that oestrogen replacement therapy is associated with risk of epithelial ovarian cancer of the endometrioid type. Using data fro m an Australian population-based case-control study, the relation between u nopposed oestrogen replacement therapy and epithelial ovarian cancer, both overall and according to histological type, was examined. A total of 793 el igible incident cases of epithelial ovarian cancer diagnosed from 1990 to 1 993 among women living in Queensland, New South Wales and Victoria were ide ntified. These were compared with 855 eligible female controls selected at random from the electoral roll, stratified by age and geographic region. Tr ained interviewers administered standard questionnaires to obtain detailed reproductive and contraceptive histories, as well as details about hormone replacement therapy and pelvic operations. No clear associations were obser ved between use of hormone replacement therapy overall and risk of ovarian cancer. Unopposed oestrogen replacement therapy was, however, associated wi th a significant increase in risk of endometrioid or clear cell epithelial ovarian tumours (odds ratio (OR) 2.56; 95% confidence interval (CI) 1.32-4. 94). In addition, the risk associated with oestrogen replacement therapy wa s much larger in women with an intact genital tract (OR 3.00; 95% CI 1.54-5 .85) than in those with a history of either hysterectomy or tubal ligation. Post-menopausal oestrogen replacement therapy may, therefore, be a risk fa ctor associated with endometrioid and clear cell tumours in particular. Add itionally, the risk may be increased predominantly in women with an intact genital tract. These associations could reflect a possible role of endometr iosis in the development of endometrioid or clear cell ovarian tumours. (C) 1999 Cancer Research Campaign.