How does early puberty increase breast cancer risk?
DZ: When a young woman reaches puberty her breast cells undergo a rapid growth and development. Puberty is a time when there are more undeveloped breast cells (stem cells) that are vulnerable to cancer-causing agents such as chemicals, viruses, radiation, and estrogens. The hormones of pregnancy, particularly estriol and progesterone, cause many of these undeveloped cells to mature to cell types that no longer can be as easily damaged and transformed into cancer cells. So when girls reach puberty earlier it opens the window of vulnerability to cancer that much wider. Henry Lemon, a research clinician and M.D., many years ago published an interesting experiment in rats that demonstrated the protective effects of pregnancy hormones like estriol. He exposed young female rats to either radiation or potent chemicals known to cause mammary cancers. As expected, nearly all of the rats developed mammary cancer, which is the equivalent of breast cancer in humans. However, if he pre-exposed thes
