Switching to the drug letrozole following 5 years of treatment with tamoxifen reduces the risk of hormone-dependent breast cancer recurrence, but not overall survival, among postmenopausal women, according to a new study in the September 7 issue of the Journal of the National Cancer Institute. The standard treatment for women with estrogen receptor-positive breast cancer is 5 years of tamoxifen. Extending the treatment past 5 years has not been associated with any additional improvement in survival, and many women experience new primary tumors and relapses after they go off the drug.Tamoxifen works by inhibiting the effects of estrogen. However, after 5 years of exposure to the drug, cancer cells may become resistant to or even dependent on it. Newer drugs, called aromatase inhibitors, can selectively inhibit the enzyme aromatase, thus lowering the levels of estrogen. Previous reports have suggested that the tumor cells involved with cancer recurrence may be vulnerable to these drugs after building up a resistance to tamoxifen.
