New data from the Intergroup Exemestane Study ( IES ) showed that hormone sensitive postmenopausal early breast cancer patients who switched to Exemestane ( Aromasin ) after 2 to 3 years of Tamoxifen were 17% more likely to be alive and were 25% less likely to have their cancer return than patients who continued on Tamoxifen for a full 5 years of therapy.
These significant survival benefits were seen in patients who are considered hormone sensitive, which represents 97% of the study population.
Although not statistically significant in the intent to treat population, 15% of patients taking Exemestane were more likely to be alive versus those that continued on Tamoxifen.
These new findings were based on nearly 5 years of follow-up after randomization in the IES trial. IES was a large randomized double blind multinational trial of postmenopausal women with early breast cancer which was designed to compare the clinical benefits of switching 2352 patients to Exemestane after 2 to 3 years of Tamoxifen versus continuing 2372 patients on Tamoxifen for a full 5 years of therapy.
The 5 year follow-up time includes a period of observation lasting over 2 years after completion of all treatment.
Earlier results of the IES trial, which led to US FDA and European regulatory approvals of Aromasin for treatment of early breast cancer, found that postmenopausal hormone receptor positive patients, which represented 85% of all patients in the trial, who switched to Exemestane reduced their risk of breast cancer recurring by 35% versus patients who stayed on Tamoxifen for 5 years. At the earlier time point, a difference in overall survival had not been seen.
At 34.5 months of follow-up, the most common side effects were mild-to-moderate and include hot flushes ( 21.2% for Exemestane vs. 19.9% for Tamoxifen ), fatigue ( 16.1% vs. 14.7% ), arthralgia ( 14.6% vs. 8.6% ), headache ( 13.1% vs. 10.8% ), insomnia ( 12.4% vs. 8.9% ), and increased sweating ( 11.8% vs. 10.4% ).
Exemestane should not be used in women who are premenopausal, are nursing or pregnant, have a known hypersensitivity to the drug, or are taking estrogen-containing agents. Dose modification is recommended for patients who are receiving certain medications, including strong CYP 3A4 inducers. In patients with early breast cancer, elevations in bilirubin, alkaline phosphatase, and creatinine were more common in those receiving Exemestane than either Tamoxifen or placebo.
Aromasin was approved in the United States in 2005 for treatment of postmenopausal women with estrogen-receptor positive early breast cancer following two-to-three years of Tamoxifen, for a combined total of five consecutive years of therapy.
Source: Pfizer, 2006