Oral contraceptives, hormone replacement therapy, and cancers of the female reproductive system

In developed countries, approximately 1.5 million women are diagnosed with cancer every year and almost half of these are cancers of the female reproductive organs. Oestrogens and progestogens, prescribed as oral contraceptives and hormone replacement therapy (HRT), are among the most commonly used medications worldwide. Oral contraceptives increase breast cancer risk while being used, although this excess risk diminishes following cessation of use. Oral contraceptives also increase the risk of cervical cancer, but they result in a long lasting reduction in the risk of ovarian and endometrial cancers. The combination of these risks means that, overall, use of combined oral contraceptives results in a net reduction in the lifetime risk of breast, ovarian and endometrial cancers. Use of oestrogen-only HRT increases the risk of breast, endometrial and ovarian cancer. Compared to oestrogen-only HRT, use of combined oestrogen-progestogen HRT results in a greater increase in breast cancer risk, a similar elevation in the risk of ovarian cancer, and a decreased or null effect on the risk of endometrial cancer. There is limited evidence available on the association between use of HRT and cervical cancer risk. Overall, the use of oestrogen-only or combined HRT results in a net increase in the risk of cancer of the breast, ovary and endometrium. Therefore, oral contraceptives and HRT have differing effects on the risk of developing reproductive system cancers. The net effect of oral contraceptives is likely to be protective in developed countries, whereas the net effect of combined HRT is to elevate the risk of reproductive system cancers.