Summary
This trial studies how well the drug tucatinib works when given with trastuzumab deruxtecan
(T-DXd). It will also look at what side effects happen when these drugs are given together. A
side effect is anything a drug does besides treating cancer.
Participants in this trial have HER2-positive (HER2+) breast cancer that has either spread to
other parts of the body (metastatic) or cannot be removed completely with surgery
(unresectable). All participants will get both tucatinib and T-DXd.