Pfizer Inc announced new, longer-term data from the Intergroup Exemestane Study (IES) showing that women who switched to exemestane (Aromasin) after taking tamoxifen for 2 to 3 years experienced a significant reduction (18%) in the risk of disease-free survival (DFS) events (hazard ratio [HR] = 0.82; 95% confidence interval [CI] = 0.73–0.92; P = .0009), compared to women who continued on tamoxifen for a full 5 years of treatment. In addition, the IES showed that exemestane prolonged overall survival (OS) in the estrogen receptor (ER)-positive/unknown population, with a 14% reduction in the risk of dying (HR = 0.86; 95% CI = 0.75–0.99; P = .04). These results demonstrate that the benefits of treatment are maintained in long term follow-up. These results were presented at the joint ECCO 15/ESMO 34 meeting in Berlin.
“These new, long-term follow-up data of the IES demonstrate a significant survival benefit for patients who switched to Aromasin compared to those who stayed on tamoxifen,” said Charles Coombes, head of the oncology department at Imperial College, London, and principal investigator of the IES. “These findings are important to patients and physicians alike as they reaffirm their confidence in switching to Aromasin after 2 to 3 years of tamoxifen.”
IES is a landmark trial with the longest follow-up of endocrine treatment in the adjuvant switch setting. It is a randomized, double-blind, multinational trial of postmenopausal women with early breast cancer. IES evaluated the clinical benefits of switching 2,352 patients to exemestane after 2 to 3 years of tamoxifen vs continuing 2,372 patients on tamoxifen for a full 5 years of therapy. The primary endpoint of the study was DFS in the intent-to-treat (ITT) population. Within the IES, 97% of the study population was ER-positive/unknown.
In postmenopausal women with early breast cancer at a median follow-up of 91 months, switching to exemestane after 2 to 3 years of tamoxifen, for a total of 5 years of treatment, was shown to result in:
• A 16% reduction in the risk of DFS events, defined as local or distant recurrence of breast cancer, contralateral breast cancer, or death from any cause, compared to staying on tamoxifen for 5 years (HR = 0.84; 95% CI = 0.75–0.94; P = .002) in the ITT population.
• An 11% relative risk reduction of death in the ITT population. A statistically significant 14% reduction in the risk of death was noted in the ER-positive/unknown population (HR = 0.86; 95% CI = 0.75–0.99; P = .04).
These DFS and OS data are consistent with the previous IES update at 55.7 months. Additionally, exemestane’s safety profile at 91 months was similar to that shown previously.