Clinical outcome of breast cancer patients has been improved by development of molecular target agents such as trastuzumab and lapatinib. However, it is still difficult to "cure" all the patients. In order to improve the results, understanding the mechanisms of action and resistance is crucial. Detection of accurate predictive markers of response to these therapies are also required. Various new drugs and their combinations are being challenged in the (pre)clinical trial along this strategy. In this review, we summarize the current findings in target therapy for breast cancer patients.