ORLANDOAn open-label randomized study comparing letrozole(Drug information on letrozole) (Femara) and anastrozole(Drug information on anastrozole) (Arimidex), the two US FDA-approved nonsteroidal aromatase inhibitors, found a higher overall response rate for letrozole as second-line therapy in women with metastatic breast cancer.
Commentators, however, discounted the difference due to the high number of receptor-unknown patients, and the session discussant called the agents "roughly similar." In response, presenter Carsten Rose, MD, PhD, stressed that the study demonstrated a high response rate for both agents, and showed that letrozole is at least as good as anastrozole in the metastatic setting.
In his presentation at the 38th Annual Meeting of the American Society of Clinical Oncology (abstract 131), Dr. Rose, director of the Department of Oncology, Lund University Hospital, Lund, Sweden, said that for some third-generation, highly selective aromatase inhibitors, "we have shown very clearly that they have at least an activity that is the same as tamoxifen(Drug information on tamoxifen) [Nolvadex]."
He suggested further that aromatase inhibitors should replace tamoxifen as the gold standard in metastatic breast cancer. Oral letrozole at 2.5 mg/d, Dr. Rose pointed out, has been shown to be consistently superior to tamoxifen as first-line therapy of hormone-sensitive advanced breast cancer in terms of time to progression, overall response rate, clinical benefit, and early survival. Relative to anastrozole, he said, letrozole has shown greater ability to inhibit aromatase in vitro, and to reduce production of estrone(Drug information on estrone), estrone sulfate, and estradiol(Drug information on estradiol).
The current multicenter, multinational trial (FEM-INT-01), sponsored by Novartis, included 713 postmenopausal women with hormone-receptor-positive or unknown metastatic breast cancer who had failed tamoxifen therapy. Participants were randomized to letrozole 2.5 mg or anastrozole 1 mg, both given once daily, with data collected to 30 months. Mean age was 63 years.
Dr. Rose noted that about 50% of patients in each group (51% letrozole, 53% anastrozole) were of unknown receptor status, which was normal trial practice at the time of the study inception outside of the United States and Canada.