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The results of a study of 1811 sets of identical and fraternal female twins suggest that early puberty may trigger breast cancer later in life in women already at risk because of their genetic makeup. In women genetically predisposed to get the disease, the rush of hormones at puberty?rather than long-term exposure?may result in breast cancer later on, according to findings published in the New England Journal of Medicine (June 3, 2003).
In the study, 1 or both twins had breast cancer. The researchers looked at their age at puberty and menopause, as well as pregnancies and other risk factors, and they looked for patterns. After reviewing the data, 1 finding stood out: For identical twins with cancer, the first twin to reach puberty was 5 times more likely to get the disease first. The link was even stronger if menstruation began before the age of 12. Menopause at an older age, fewer children, and a later first pregnancy made no difference.
Because identical twins share genes, the researchers believe that there was a hereditary reason behind the susceptibility to the onset of hormones. Thus far, scientists have uncovered a few gene mutations that up the risk of breast cancer. Although the focus has been on genes related to estrogen levels, the researchers in this new study suggest also looking for genes that affect the sensitivity of immature breast cells at the onset of puberty.