However, some researchers have found that tamoxifen can increase the risk of abnormal uterine bleeding, which can indicate uterine abnormalities or even endometrial cancer, cancer of the lining of the uterus. Now British researchers are investigating whether an intrauterine device can help reduce the chances of uterine abnormalities in women who take tamoxifen. Tamoxifen helps fight breast cancer by blocking estrogen from estrogen-receptors in breast cancer cells. While tamoxifen fights estrogen in breast cancer cells, it acts as a weak estrogen in the uterus. Tamoxifen can stimulate the growth of endometrial cells and increase the risk of endometrial cancer in some women.
Progesterone is a hormone that can counteract the effects of estrogen on the uterus.
The T-shaped intrauterine device is currently used as a form of birth control in Asia and Europe. Mirena, the pharmaceutical company that makes the intrauterine device, is applying for FDA approval of the device in the United States for use as contraception. To conduct their study, the researchers studied 122 post-menopausal women who had taken tamoxifen for at least one year in addition to other breast cancer treatments such as surgery. Half of the women on tamoxifen were fitted with the intrauterine device while the other half of the women continued taking tamoxifen without the device. However, the researchers warn that their research is preliminary and needs to be confirmed in a large clinical trial where the effectiveness of the intrauterine device can be evaluated for the duration of tamoxifen treatment.