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Twin Study Shows New Breast Cancer Risk

Hormonal Surges in Adolescence Put Some Women at Risk

A New Breast Cancer Risk continued...

"Within these pairs, the factors usually found to be the strongest predictors -- age at first full-term pregnancy, parity, and age at menopause -- were completely unrelated to the sequence of diagnoses," write the researchers.

However, among identical twin pairs in which only one twin had breast cancer, a later first pregnancy, fewer children, and later menopause were associated with an increased risk of breast cancer, but age of puberty was not.

Researchers say that because identical twins share the same genes, those twins who both develop breast cancer are thought to have a hereditary form of breast cancer. But when only one twin of a pair gets breast cancer, the disease is thought to be sporadic and influenced less by genetic factors.

Therefore, researchers say the study suggests that most cases of hereditary breast cancer are not related to total hormone exposure during a woman's lifetime, but to an unusual susceptibility to the hormonal surge of puberty.

Could Affect Many

If those findings hold true, researchers say a substantial subgroup of women are at higher risk for breast cancer because of very early puberty, and the problem will continue to grow in significance as the age of puberty continues to decline in the U.S.

In an editorial that accompanies the study, Patricia Hartge, ScD, of the National Cancer Institute, says more research will be needed to confirm these results. But the study provides intriguing evidence that two distinct pathways to breast cancer may exist.

"As studies succeed in finding gene-hormone interactions, we can expect to illuminate the pathways to breast cancer and reduce the chances that it will develop," writes Hartge.

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