In a separate study reported at the meeting, researchers found that doubling the dose of an existing breast cancer drug, Faslodex (fulvestrant), lengthened women's lives by a few months.
Like the other trial, this one focused on older women with advanced ER-positive cancer. Faslodex is an injected form of hormonal therapy that works by blocking the effects of estrogen on breast cancer cells; it's given to postmenopausal women whose cancer has worsened despite anti-estrogen therapies such as tamoxifen.
Among more than 700 women in the trial, those randomly assigned to a 500-milligram dose of Faslodex typically lived about four months longer: 26 months versus 22 months among women given the standard 250-milligram dose.
The higher dose extended lives without increasing side effects, said the researchers, led by Dr. Angelo Di Leo, head of medical oncology at the Hospital of Prato in Italy.
Faslodex commonly causes side effects such as nausea, vomiting, diarrhea, headaches and hot flashes, and occasionally more serious problems, such as blood clots. In this trial, between 1 percent and 2 percent of women in each group had a serious side effect attributable to the medication.
The trial was sponsored by AstraZeneca Pharmaceuticals, which makes Faslodex.
The higher Faslodex dose has already become the "standard of care," based on earlier findings from the trial, said Dr. Kimberly Blackwell, director of the Duke Breast Cancer Clinic and a professor of medicine at Duke University School of Medicine.
Blackwell, who was not involved in either new study, was more excited about the experimental Pfizer drug.
"We always want to be cautious about a trial that involves fewer than 200 patients," Blackwell said. But, she added, "if this is confirmed in the Phase 3 trial, it could have a big impact on how we treat patients."
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