A study of the Women's Health Initiative raveled that the therapy of estrogen-plus-progestin hormone replacement raises women’s exposure to breast cancer.

The study took data of 16,000 women who were divided in two groups. One group was treated with the hormone Prempro and the other group received a placebo in a period over 5 years and six months.

Results highlight the fact that not only cancer risk but also the death rates might increase for patients who underwent the hormone therapy.

One explanation in the Journal of the American Medical Association is the causal effect of hormones triggering the growth of tumors.

Especially women, who undergo a hormone therapy in order to regulate their post-menopausal conditions, are endangered to get affected by breast cancer as a consequence.

Approximately 15% to 20% of US women, already having had their menopause, are currently treated with Prempro. The producer of the drug, Pfizer, declares that the results of the research have been included in the drug’s label over 15 years now. "This analysis does not alter that risk, nor does it dispute hormone therapy's effectiveness”.

The Women's Health Initiative’s recommendations led to abandoning of hormone therapy among US women. As a result, the breast cancer rate decreased immediately.