Pilot Study of Paclitaxel Plus Pembrolizumab in Metastatic HER2-Negative Breast Cancer

This is an open-label randomized pilot research study to determine if the study drug, pembrolizumab, is safe to use in combination with a chemotherapy drug called paclitaxel. This study will have the following two regimens: Cohort A) phased regimen of pembrolizumab in which paclitaxel is followed by paclitaxel plus pembrolizumab and Cohort B) concurrent regimen of paclitaxel plus pembrolizumab. A total of 40 evaluable subjects will be enrolled over an enrollment period of 18-24 months. The study is planned to enroll approximately 20 evaluable subjects in each treatment cohort.