ARIMIDEX: A potent and selective aromatase inhibitor for the treatment of advanced breast cancer

Aromatase inhibitors have been available for a number of years and their ability to reduce circulating estradiol levels has been shown to produce clinical benefit in women with advanced breast cancer. Until recently, the only commercially available aromatase inhibitor was aminoglutethimide. Although aminoglutethimide has been shown to be efficacious in the treatment of advanced breast cancer, it does cause significant toxicity and requires the use of concomitant hydrocortisone therapy. Anastrozole is one of a new class of potent aromatase inhibitors able to suppress estradiol to the limit of detection of sensitive assays without suppressing adrenal steroidal synthesis. Two large clinical trials (n = 764) conducted in the U.S.A. and in Europe evaluated two doses of anastrozole, 1 and 10 mg a day, compared to megesterol acetate, 40 mg four times a day, in postmenopausal women who had progressed while on tamoxifen. Response rates and time to progression with anastrozole were similar to those of megesterol acetate. Objective responses (CR + PR) were 10.3%, 8.9% and 7.9% in the 1 and 10 mg of anastrozole and megesterol acetate treatment groups, respectively. Another 25.2%, 22.6% and 26.1% had stable disease for over 24 weeks on 1, 10 mg anastrozole and megesterol acetate, respectively. Anastrozole and megesterol acetate were well tolerated; however, more patients had significant weight gain on megesterol acetate than with anastrozole treatment. The weight gain seen with megesterol acetate continued to increase over time. Anastrozole has a better therapeutic index (fewer side-effects) and has recently been approved by the FDA and a number of other regulatory agencies around the world for the treatment of advanced breast cancer.