There are more than 18 sub-types of breast cancer. Risk factors for developing breast cancer include: female sex, obesity, lack of physical exercise, drinking alcohol, hormone replacement therapy during menopause, ionizing radiation, early age at first menstruation, having children late or not at all, and older age. Excessive estrogens are involved in breast, uterine and ovarian cancer development. Estrogen receptors (ER) are hence important targets for drugs that can be used to control diseases such as cancer and disorders caused by hormonal imbalances and inflammatory reactions.