ATLANTA ? Switching to Aromasin (exemestane), an aromatase inhibitor, as adjuvant therapy for breast cancer after two to three years of tamoxifen may increase disease-free survival, according to mature results of a trial of postmenopausal women.
ATLANTA, June 4 ? Switching to Aromasin (exemestane), an aromatase inhibitor, after two to three years of adjuvant therapy with tamoxifen for early stage breast cancer may increase disease-free survival, according to results from a trial of postmenopausal women.
The first mature follow-up analysis of data from the Intergroup Exemestane Study (IES) found a significant increase in disease free survival for women treated with Aromasin versus those who continued on tamoxifen, according to results reported at the American Society of Clinical Oncology meeting.
After five years of treatment with Aromasin following initial tamoxifen therapy, there was a 24% reduction in the relative risk of disease relapse or dying for patients treated with Aromasin versus women continued on tamoxifen for five years, said Judith Bliss, M.D., of the Institute of Cancer Research in Sutton, England.
Disease-free survival was 83.6% for women who received Aromasin versus 80.2% for women taking tamoxifen, or an absolute difference of 3.4%, she said. The hazard ratio was 0.76 (95% C.I. 0.66-0.88) log-rank test P=0.0001.
But that difference has not yet translated into a statistically significant difference in overall survival, although there was a 15% (range 2% to 29%) reduction in the risk of dying (P=0.08).
However, when Dr. Bliss and colleagues analyzed the data by estrogen-receptor status, there was a 17% (range 0 to 31%) reduction in risk of dying, which was statistically significant (P=0.05). for patients treated with Aromasin.
The IES study randomized 2,352 post menopausal women with early-stage breast cancer to two to three years of Aromasin following two to three years of tamoxifen and 2,372 women to continued tamoxifen therapy.
The endpoint of this analysis was the number of events in the Aromasin arm versus the tamoxifen arm. Intention-to-treat analysis found 354 events in the Aromasin arm versus 454 events in the tamoxifen arm. At five years there were 222 deaths in the Aromasin arm versus 261 deaths in the tamoxifen arm.
"Although I'm a statistician, I'm not all that wedded to a specific P value," said Dr. Bliss. "When I see a 15% reduction in risk of dying, I consider that to be evidence of a significant effect."
Oncologist Julie Gralow, M.D., of the University of Washington and the Fred Hutchinson Cancer Center in Seattle, agreed. She said, however, that while head-to-head trials of aromatase inhibitors and tamoxifen have demonstrated a benefit in reduction of risk of recurrence for agents like Aromasin "no survival benefit has been observed."
"This is a first," Dr. Gralow said, but she suggested that the data indicate that the survival benefit may "be due to this switching strategy: first tamoxifen, then [Aromasin]."
Robert Mayer, M.D., of Harvard Medical School, was not persuaded by results. "These data do not show a survival advantage," he said in an interview. "They indicate a reduction in events in the [Aromasin] arm, but that has not matured into a survival advantage."