Lapatinib is an oral, small-molecule, dual kinase inhibitor that targets both HER2 and the EGF receptor. Lapatinib was approved in June 2008 in Europe for the treatment of advanced HER2-positive breast cancer. Promising results in trastuzumab-refractory metastatic breast cancer were obtained from Phase I, II and III studies in combination with chemotherapy. Diarrhea and rash are the most common side-effects and are mostly moderate and treatable. Cardiac toxicity occurs rarely and mostly as an asymptomatic and reversible decrease of left ventricular ejection fraction. Unlike trastuzumab, some data show that lapatinib could cross the blood–brain barrier, with some evidence of activity in treating or preventing brain metastases. Its evaluation is actively ongoing, in combination with trastuzumab and in the adjuvant setting.