Sept. 20, 2006 -- For more than two decades, tamoxifen has been the estrogen-targeting drug of choice for treating breast cancer. But evidence is mounting that newer drugs help patients with advanced disease live longer.
An analysis of 23 studies comparing the newer therapies, known as aromatase inhibitors, with standard hormonal treatments, suggests a clear survival advantage for women taking the newer drugs. Aromatase inhibitors work by lowering the amount of estrogen in the body.
From the pooled analysis, the researchers estimate that an advanced breastcancercancer patient normally expected to live 2.5 years would get, on average, an additional four months of life by taking a third-generation (the newest) aromatase inhibitor instead of tamoxifen.
For a patient with an expected 10-month survival, there would be about a one-month increase.
"I would say that the evidence is fairly convincing that the third-generation aromatase inhibitors can improve survival in patients with advanced disease," John P.A. Ioannidis, MD, co-author of the analysis, tells WebMD.
Aromatase Inhibitors Widely Used
Aromatase inhibitors are now widely used in the U.S. to treat both early stage and advanced hormone-receptor-positive breast cancers -- cancers that use estrogen to grow -- in postmenopausal women.
However, a clear survival advantage for this treatment over tamoxifen has not been proven.
In an effort to better understand the effectiveness of aromatase inhibitors in patients with advanced disease, Ioannidis and colleagues analyzed studies that compared the newer drugs head to head with tamoxifen.
The pooled studies included 4,559 patients treated with aromatase inhibitors and 3,945 patients treated with tamoxifen or other standard hormone therapies.
The researchers found no survival advantage for patients taking the earliest aromatase inhibitors over tamoxifen.
The researchers concluded that these drugs should be considered the accepted initial treatment for patients with advanced breast cancer.
Their findings are published in the Sept. 20 issue of the Journal of the National Cancer Institute.
Tamoxifen Still Needed
Daniel Hayes, MD, who directs the breast cancer program at the University of Michigan Comprehensive Cancer Center, says the evidence has long pointed to a modest survival benefit for advanced breast cancer patients taking aromatase inhibitors.
He adds that there is increasingly strong evidence the newer drugs are also more effective than tamoxifen in patients with less advanced disease.
But that doesn't mean tamoxifen no longer has a place in breast cancer treatment, he tells WebMD.
Individual patients may still respond better to tamoxifen or they may experience fewer side effects on the older hormone therapies, he says. And it may be that patients whose cancers progress while they are taking aromatase inhibitors can benefit from switching to tamoxifen.
"These are all unanswered questions at this point," Hayes says. "We may be able to individualize treatment with these two drugs in the future."
Eric Winer, MD, who directs the Breast Oncology Center at Boston's Dana-Farber Cancer Institute, agrees.
"Ultimately, the hope is that we will be able to identify tumor or patient characteristics that can guide us in the choice of treatment," he tells WebMD. "It may be that some patients will benefit most from treatment with an aromatase inhibitor immediately, while another will do better with a few years of tamoxifen, followed by an aromatase inhibitor."
The American Society of Clinical Oncology now recommends the use of aromatase inhibitors for the treatment of hormone-receptor-positive tumors in postmenopausal women, either as first-line or second-line treatment. Winer chaired the ASCO panel which made the recommendation.
"These drugs are clearly beneficial, but the jury is still very much out on whether patients should start with these drugs and take them for five years, or whether taking tamoxifen for a few years followed by an aromatase inhibitor may be beneficial."