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Aromatase Inhibitors ‘Roughly Similar’ in Metastatic Breast Cancer

Aromatase Inhibitors ‘Roughly Similar’ in Metastatic Breast Cancer

ORLANDO—An open-label randomized study comparing letrozole (Femara) and
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 [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, estrone sulfate, and estradiol.

FEM-INT-01

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.

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