Progestins increase chances of cancer metastasizing, finds study
 

After menopause, 6 to 10 million women take hormone therapies, which are often a combination of estrogen and progestin, to replace hormones lost from inactive ovaries. Progestin is a hormone that is used to counteract the potentially negative effects of estrogen therapy on the uterus. In studies sponsored by the National Institutes of Health, evidence has been found that estrogen and progestin in hormone therapies increase the risk of breast cancer in post-menopausal women.

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