Lapatinib: in postmenopausal women with hormone receptor-positive, HER2-positive metastatic breast cancer.

Lapatinib is an orally active, low molecular weight, reversible inhibitor of the intracellular tyrosine kinase domains of both human epidermal growth factor receptor (HER) type 1 (HER1) and type 2 (HER2). In a large phase III trial (EGF30008) in 1286 postmenopausal women with hormone receptor (HR)-positive, metastatic breast cancer who had not received previous therapy for advanced or metastatic disease, the primary endpoint of median progression-free survival in a HER2-positive population of 219 women was significantly longer with lapatinib plus letrozole than with letrozole plus placebo (8.2 vs 3.0 months). Overall response rates (28% vs 15%) and clinical benefit rates (responsive or stable disease for >or=6 months; 48% vs 29%) were also significantly higher with lapatinib plus letrozole than with letrozole plus placebo. Most adverse events associated with lapatinib when administered in combination with letrozole were mild to moderate in severity in the EGF30008 phase III trial.