Breast Cancer Risk and Estrogen + Progestin Hormone Therapy
Posted May 10 2010 7:32am
Hormone replacement therapies were designed to aid women through the transition from premenopausal to postmenopausal stages of life by reducing common menopausal discomforts. While some hormone therapies were based on estrogen only, many were a combination of estrogen plus a progestin that was designed to protect women from potential negative effects of estrogen. By now it is well known that the Women's Health Initiative study showed that estrogen + progestin hormone therapy has a number of negative health effects, including a 24% increase in breast cancer risk over about a 5 year period. The reasons for this increased breast cancer risk are still being investigated and two new studies suggest some possible explanations.
In one breast cancer study , researchers examined changes in breast density over a 2 year period in postmenopausal women treated with a low dose hormone replacement therapy (1 mg estrogen + 2 mg drospirenone, a synthetic progestin). The results of this study showed that radiologist-assessed breast density increased substantially over the 2-year study period in women on the hormone therapy.
In a second breast cancer study , investigators examined the effect of several progestins on breast cancer tumors in an animal breast cancer model. The results of these studies showed that all of the progestins tested increased the number of blood vessels responsible for allowing cancer cells to spread, thereby increasing the risk for metastasis. Additionally, these breast cancer researchers reported that if the tumor suppressor protein p53 was not working properly, the progestins induced the formation of new blood vessels within the breast cancer tumors, an important requirement for additional tumor growth.
Overall, these results continue to confirm the increased risk of breast cancer with the use of hormone therapy that contains a progestin. While hormone therapy is still prescribed for the relief of menopausal discomforts, the FDA recommends that hormone therapy be used at the lowest effective dose for the shortest period of time necessary. More and more studies are showing that progestins increase breast cancer risk through a variety of breast cancer risk factors, including inducing tumor blood vessel, increasing breast density, and increased rates of atypical ductal hyperplasia.