A Study Of Pembrolizumab In Combination With Trastuzumab-DM1

This research study is a Phase I clinical trial, which tests the safety of an investigational intervention and also tries to define the appropriate dose of the investigational intervention to use for further studies. "Investigational" means that the intervention is being studied. It also means that the FDA (U.S. Food and Drug Administration) has not approved the combination of Pembrolizumab and T-DM1 for use in patients, including people with your type of cancer. This study will determine what amount (or dose) of Pembrolizumab and of T-DM1 is safe for people to take and what effects, good or bad, this combination may have on participants and their disease. The FDA has not approved Pembrolizumab for this specific disease but it has been approved in the United Sates for the treatment of other types of cancer. The FDA has approved Trastuzumab emtansine (T-DM1) as a treatment option for this type of breast cancer The combination of Pembrolizumab and T-DM1 is investigational. It is thought that together these drugs to help get the immune system to attack tumor cells and kill cancer cells that have the HER2 protein. However, it is not known if giving the two study drugs at the same time will have a better anti-cancer effect than giving each treatment on its own.