Exemestane is a steroidal agent which causes inactivation of the
aromatase enzyme by binding irreversibly to the substrate binding site. Oral
exemestane 25 mg/day inactivates peripheral
aromatase activity (approximately 98% inactivation) and reduces basal plasma
estrone,
estradiol and
estrone sulphate levels by 85 to 95% in postmenopausal women with advanced
breast cancer. Phase II trials indicate that oral
exemestane 25 mg/day is an effective second- or third-line agent in the treatment of postmenopausal women with advanced
breast cancer (achieving an objective response in up to 28 and 26% of patients, respectively). Results from a phase III trial indicate that
exemestane achieves a similar objective response rate to
megestrol as a second-line
therapy; however,
exemestane achieved a significantly longer duration of overall success, time to
disease progression and survival time.
Exemestane is at least as well tolerated as
megestrol, but is associated with significantly fewer bodyweight changes, mainly bodyweight gain (> or = 10%). Other common adverse events are hot flushes,
nausea and
fatigue.