Another Study Finds Increased Breast Cancer Risk from Hormone Therapy

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A new study published in Cancer Epidemiology, Biomarkers & Prevention concluded that the risk of breast cancer varies by personal characteristics but this study reinforced that there is an increased risk of breast cancer from hormone use and further studies are needed to address how specific that risk is. Hormone replacement therapy among 2,857 women were analyzed for almost 10 years and it was found that when compared with women who never used hormone therapy, women who used estrogen therapy for more than 15 years had a 19 percent greater risk of developing breast cancer. For those who used a combined program of estrogen and progestin for 15 or more years the risk increased 83 percent. Thus, the breast cancer risk was highest for the combined hormone therapy group.
Results also showed that breast cancer risk was dependent on body mass index (BMI) because those with a BMI under 30 seemed to have an increased risk with combined therapy and it was highest for women with a BMI under 25. On the other hand obese women with a BMI over 30 had no further risk associated with using combined hormone therapy. The risk for these breast tumors were for tumors that were positive for both estrogen and progestin receptors and were weaker for HER2 negative tumors. Further research is need to answer lingering questions for this complex association.

However, in another study published in the September issue of Cancer Prevention Research researchers found that breast cancer risk varies by the type of progestin used in hormone therapy. In the study they compared the effect of 4 progestins on breast cancer in animal models. Progestins used included 1) synthetic progestin medroxporgresterone acetate (MPA), 2) norgesterel (N-EL), 3) norethindrone (N-ONE) and 4) megestrol acetate (MGA). The MPA progestin in Prempro is most often used by women in the United States for Hormone Therapy. The authors concluded “although previous studies using an animal model for breast cancer found the MPA functions as a tumor promoter, this study showed that N-EL and N-ONE……. strongly inhibited tumor development.” Progestins seems to have tumor stage specific effects that determines whether they function as tumor promoters or protectors. Those such as N-EL and N-ONE seem to prevent breast cancer in women without a history of or family history for breast cancer and for post menopausal women who are at increased risk due to combined estrogen/progestin (MPA) hormone therapy.

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