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Letrozole Superior to Tamoxifen Regardless of Hormone Receptor Status: Presented at SABCS

By Charlene Laino

SAN ANTONIO, TX -- December 13, 2002 -- The nonsteroidal aromatase inhibitor letrozole is significantly superior to tamoxifen as first-line treatment of metastatic breast cancer regardless of whether one or both hormone receptors are positive or both are unknown, a new study suggests.

Alain Monnier, MD, Head of Medical Oncology and Radiotherapy at the Centre Hospitalier André-Boulloche in Montbeliard, France, presented the results at a poster session on December 11^th here at the 25^th Annual San Antonio Breast Cancer Symposium.

After letrozole demonstrated superior efficacy over tamoxifen in the treatment of postmenopausal women with advanced breast cancer in a large, double-blind, randomised, phase III trial, the investigators sought to determine whether receptor status would influence outcome.

Nine hundred women with advanced breast cancer participated in the prospective trial. They were randomly assigned to treatment with either 2.5 mg a day of letrozole or 20 mg a day of tamoxifen. At first progression, women could be switched to the alternative treatment in a double-blind fashion or allowed to go on an alternative therapy at the discretion of the investigator. Patients who crossed over could also be switched to an alternative therapy at second progression.

At a median follow-up of 32 months, time to progression was a median of 6.0 months for patients treated initially with tamoxifen, compared with a median of 9.4 months for those initially treated with letrozole -- a 57 percent difference.

Multivariate analysis showed that neither oestrogen receptor status nor progesterone receptor status alone significantly influenced outcome.

Patients with tumours positive for both steroid receptors, however, achieved a greater time to progression, particularly when treated with letrozole. Time to progression was a median of 11.9 months for such women treated with letrozole, compared with 6.0 months for those treated with tamoxifen (p=0.0001). The objective response rate was 37 percent in such women treated with letrozole, compared with 21 percent in those given tamoxifen (p=0.0007).

Dr. Monnier noted that the results are different from those obtained with anastrozole, which demonstrated superiority to tamoxifen only in women with hormone receptor-positive tumours.

Although no direct comparison is available, the data suggest that letrozole may be superior to anastrozole in the treatment of women with metastatic breast cancer and unknown receptor status, he said, even though most studies show that about two-thirds of so-called receptor-unknown patients are actually positive.

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