To understand why women who begin menstruating at a young age are at a slightly elevated risk of developing breast cancer, one must understand the role of estrogen. Estrogen in itself does not cause cancer—it is an essential part of a woman’s physiology. However, estrogen's principal function is to speed the process of cell proliferation. So it follows that estrogen can increase the chance of a mutation occurring and/or encourage the growth of cancerous cells once they appear. The more estrogen a woman is exposed to during her lifetime, the greater the opportunity for the hormone to promote the growth of a tumor. This is why women who begin menstruation at an early age are at greater risk of developing breast cancer—they have had a longer lifetime exposure to estrogen. |
