Estrogen and Cancer

Estrogen is actually a family of related molecules that stimulate the development and maintenance of female characteristics and reproduction.  The most common types are estrone and estradiol.  They are both produced by the ovaries, and estrone is made in the adrenal glands, as well as other organs. Lastly, estriol is the third form of estrogen and it's created by the placenta.  

Two targets of estrogen are the uterus and breast.  Usually, estrogen promotes healthy cell growth, but there are times cell proliferation is stimulated and can raise the risk of developing breast or uterine cancer. Breast cancer rises with menstruation at an early age, late age at menopause, later age at first full-term pregnancy, and few or no pregnancies.

Some studies have pointed at the fact that body fat and menopause may be a significant factor in the estrogen-cancer connection.  This is because that after menopause the adrenal glands continue to produce slight amounts of androstenedione, which is then converted into estrogens in fat tissue.  This increase in androstenedione may be why menopause and obesity are associated with higher estrogen levels and therefore a risk of breast cancer. Plus, obesity is associated with an increase of tumor burden in women who are diagnosed with breast cancer.

Reference:  INR Seminars, Estrogen and Cancer, http://blog.inrseminars.com/estrogen-and-cancer/