Palbociclib and Letrozole in Advanced Breast Cancer.

Abstract (PubMed)

A phase 2 study showed that progression-free survival was longer with palbociclib plus letrozole than with letrozole alone in the initial treatment of postmenopausal women with estrogen-receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer. We performed a phase 3 study to confirm and expand the efficacy and safety data. In this double-blind study, 666 postmenopausal women with ER-positive, HER2-negative breast cancer were randomly assigned 2:1 to receive palbociclib plus letrozole or placebo plus letrozole. The primary end point was progression-free survival (PFS). The median PFS was 24.8 months in the palbociclib-letrozole group versus 14.5 months in the placebo-letrozole group (hazard ratio 0.58; 95% CI 0.46–0.72; P<0.001). The most common adverse events with palbociclib were neutropenia (grade 3 or 4 in 66.4%), leukopenia (25.2%), and fatigue (1.5%). Palbociclib plus letrozole significantly improved PFS in postmenopausal women with previously untreated ER-positive, HER2-negative advanced breast cancer.