Alliance A011801, “The CompassHER2 trials (COMprehensive use of Pathologic Response ASSessment to optimize therapy in HER2-positive breast cancer): CompassHER2 Residual Disease (RD), a double-blinded, phase III randomized trial of T-DM1 and placebo compar

The purpose of this study is to compare the usual treatment with T-DM1 alone to T-DM1 plus tucatinib. The addition of tucatinib to the usual treatment could prevent the breast cancer from returning. But it could also cause side effects, which are described in the risks section below.

This study will help the study doctors find out if this different approach is better than the usual approach. To decide if it is better, the study doctors will be looking to see if the study approach decreases the likelihood of the breast cancer returning by 5%.

T-DM1 is already approved by the FDA for use in patients with HER2-positive cancer. Tucatinib has been FDA-approved to treat HER2-positive breast cancer that has spread to other parts of the body, but not for patients with early stage HER2-positive breast cancer.