HER2CLIMB-02: Tucatinib or Placebo in Combination with Ado-Trastuzumab Emtansine (T-DM1) for Patients with HER2-positive Breast Cancer (H-46822)

This study is being done to find out if tucatinib plus T-DM1 works better to treat breast cancer than T-DM1 alone.

Tucatinib is a type of drug called a small-molecule inhibitor. It is designed to find and stick to breast cancer cells that make the HER2 protein. When this happens, the breast cancer cells can't make any more breast cancer cells, which helps keep breast cancer cells from spreading.

Participants are randomized to one of two groups - one group will receive tucatinib + T-DM1 and one group will receive a placebo + T-DM1. Both tucatinib and T-DM1 are approved by the FDA for the treatment of breast cancer.