Medical research suggests that cancers of the reproductive organs may be affected by naturally occurring steroid hormones produced by the endocrine system. These hormones stimulate reproductive organ cells to divide and grow. In women, relatively high or long exposure to the female sex hormone estrogen seems to increase the risk of breast and uterine cancers.
Thus, early age at first menstruation, late age at menopause, having children after age 30, and never having children, all of which affect the duration of estrogen exposure in the body, increase the risk for these cancers. Some evidence also suggests that estrogen replacement therapy (ERT), in which women take estrogen to offset the unpleasant effects of menopause, may also increase the risk of some cancers of the reproductive organs.
The risk appears to go down significantly, however, when estrogen and another female sex hormone, progesterone, are taken together. At one time studies showed a link between birth control pills and cancer. However, these studies examined early forms of birth control pills, which contained high levels of estrogen. Today’s birth control pills contain progesterone, as well as lower levels of estrogen, and carry very little risk of cancer. Male sex hormones, particularly testosterone, also appear to play a role in cancers of the male reproductive organs, but this role is not yet well understood.