The purpose of this study is to test the safety of different doses of ARRY-380 in combination
with trastuzumab. Trastuzumab is an FDA approved drug for the treatment of HER2 metastatic
breast cancer. However, the combination of ARRY-380 and trastuzumab has not yet been tested.
Both agents block the HER2 receptor, which is thought to be overactive in HER2-positive
breast cancer. It is thought that ARRY-380 and trastuzumab might work together because they
attach to different parts of the HER2 receptor and prevent it from functioning. Because HER2
positive breast cancer contains high levels of HER2 receptor, but normal cells in your body
generally do not, the drugs may be able to "target" the cancer cells. In addition, in
laboratory studies, ARRY-380 appears to have some penetration into the brain.