"The combination of oral temsirolimus and letrozole did not improve progression-free survival of postmenopausal women with locally advanced of metastatic breast cancer compared to letrozole alone," reported José Baselga, MD, chairman and professor of medicine, Vall d'Hebron University Hospital, Barcelona, Spain.

Dr. Baselga was one of the many international co-authors of the study, presented in a poster presentation on December 17^th.

In the phase 3 study, 556 women were randomly assigned to receive both temsirolimus 30 mg daily for 5 days every 2 weeks and letrozole (Femara) 2.5 mg daily, and another groups of 556 women were assigned to receive only letrozole 2.5 mg daily.

Temsirolimus is a specific inhibitor of mTOR (mammalian target of rapamycin), a protein that is required to sustain tumor growth. Researchers theorized that temsirolimus could enhance the tumor-fighting qualities of other anticancer agents such as letrozole.

In the study, 13 women or 2% of the total cohort were able to achieve a complete response when taking both drugs compared with 11 women (2%) who were taking letrozole alone. In each group, another 137 women were able to achieve a partial response.

"A greater percentage of patients treated with the combination (29%) had grade 3 [adverse] events compared with those patients treated with letrozole alone (18%)," Dr. Baselga stated.

Because of the failure of the combination to show a difference in efficacy and its poorer tolerability profile, the study was stopped after 22 months upon the recommendation of the Data Monitoring committee. The study was planned to continue until 726 events progression or death had occurred. It was stopped after 380 events were recorded.

A previous phase 2 study had appeared to show benefits of the combination.

The researchers suggested that temsirolimus' role in the treatment of patients with advanced breast cancer could be explored further in biological subsets.

The study sponsored by Wyeth Pharmaceuticals.


[Presentation title: Phase 3 Study of Temsirolimus With Letrozole or Letrozole Alone in Postmenopausal Women With Locally Advanced or Metastatic Breast Cancer. Abstract 6091]

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