The international study, published in The New England Journal of Medicine, included more than 6,100 postmenopausal women who had breast cancer that was sensitive to the hormones estrogen or progesterone.
After the women finished their breast cancer treatment, they were assigned to one of the following plans:
- Take tamoxifen for five years
- Take Femara for five years
- Take tamoxifen for two years, then Femara for three years
- Take Femara for two years, then tamoxifen for three years
The women didn't know which pills they were taking.
Tamoxifen and Femara work differently. Tamoxifen blocks the action of estrogen in the body.
The new study shows that over about six years, the women's odds of cancer-free survival were equally good taking Femara alone or taking either tamoxifen first and Femara later or vice versa.
There was no significant difference in overall survival between women who took Femara alone compared to women who took tamoxifen alone for five years, report the researchers, who included Henning Mouridsen, MD, chair of the Danish Breast Cancer Cooperative Group.
The new study shows that the drugs' side effects were in line with known risks; no unusual adverse events were reported.
The study was funded by Novartis, the drug company that makes Femara. In the journal, Mouridsen and several other researchers disclose ties to Novartis. Femara was the only aromatase inhibitor included in the study.