Estrogen

Estrogen (or oestrogen) is a hormone or chemical messenger produced in both men and women. It is the main sex hormone in women and is essential to the menstrual cycle. While estrogens are present in both men and women, they are usually present at significantly higher levels in women of reproductive age. They promote the development of female secondary sex characteristics, such as breasts, a widened pelvis, and increased amounts of body fat in the buttock, thigh and hip region. Estrogen also contributes to the fact that women have less facial hair and smoother skin then men.

About 80% of breast cancers, once established, rely on supplies of the hormone estrogen to grow: they are known as hormone-sensitive or hormone-receptor-positive cancers. Suppression of production in the body of estrogen is a treatment for these cancers.