Pharmaceutical company Novartis has called an early end to its phase III study of the effectiveness of Afinitor (everolimus) tablets in combination with exemestane in women with metastatic breast cancer, after an interim analysis revealed that the regimen significantly extended progression-free survival (PFS) compared with placebo plus exemestane. PFS was the primary end point of the trial.

The randomized, double-blind study—known as BOLERO-2 (Breast cancer trials of OraL EveROlimus-2)—involved more than 700 postmenopausal women, at 195 sites worldwide. All participants had estrogen receptor-positive (ER+), human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer whose disease has progressed despite initial endocrine therapy with the nonsteroidal  aromatase inhibitors letrozole or anastrozole. Everolimus targets the mTOR protein in cancer cells, which is an important regulator of tumor cell division, blood vessel growth, and cell metabolism.

Patients received either continuous therapy with everolimus 10 mg/day orally or placebo plus oral exemestane 25 mg/day. Twice as many patients were randomized to the everolimus group than to the placebo group. Women who had already undergone more than one regimen of chemotherapy for advanced breast cancer were excluded from enrollment.

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A statement from Novartis did not specify the PFS rates in the two sets of patients, nor did it provide data on the secondary end points of overall survival, overall response rate, incidence of adverse events, patient-reported outcomes, and clinical benefit rate. The company did note that results would be presented at an upcoming medical conference, and that worldwide regulatory submissions may take place by the end of 2011 (

The company also affirmed that everolimus is being investigated for the treatment of patients with HER2-positive advanced breast cancer.