Postmenopausal hormone therapy and cancer risk

Postmenopausal Hormone Replacement Therapy has been implicated in the development 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.