Endogenous Estrogens
What are endogenous estrogens?
Endogenous estrogens are the female sex hormones the body produces as part of the menstrual cycle. Longtime exposure to endogenous estrogens increases the risk of breast cancer. Women who start menstruating before age 12 or begin menopause after age 55 generally have more monthly cycles and therefore a longer lifetime exposure to estrogen. This tends to increase their risk of breast cancer. Women who have never had children or who start their families late also have a higher lifetime exposure to estrogens. Click to Reproductive History.
How do estrogens work?
Before menopause, a woman's ovaries manufacture estrogens, creating roughly equal quantities of estradiol and estrone. Estradiol is the more powerful of the two. Both forms of estrogen attach to estrogen receptors in body cells. When an estrogen attaches to receptors in breast cells, it sends the message "proliferate" (grow new cells). These new cells form in the ductal tissues in the breast to prepare for a pregnancy that might occur during that particular monthly cycle. These new cells become important for lactation and milk production.
Why does greater exposure to estrogens increase the risk of breast cancer?
The same characteristic that makes estrogen central to pregnancy and reproduction also makes it increase the risk of cancer: estrogen stimulates cell growth. This characteristic increases risk because cell divisions increase the likelihood that a cell will become abnormal and possibly cancerous. Cell divisions also increase the likelihood that such abnormalities will be passed on as the cells divide.
Cells can develop cancer-causing mutations for any number of reasons: exposure to carcinogens, exposure to radiation, or simply through the process of cell division itself. When a cell containing a mutation divides, that mutation is passed on to the daughter cells. Rapid cell division means more frequent transmission of a mutation, if one has occurred. Precancerous conditions can develop and eventually turn into a full-fledged cancer.
