Standard of Care Chemotherapy Plus Pembrolizumab for Breast Cancer

Inclusion Criteria: Be willing and able to provide written informed consent/assent for the trial. * Be 18 years of age on day of signing informed consent. * HER2-negative breast cancer (defined by immunohistochemistry (IHC) 0-1 (or) IHC 2 and in situ hybridization (ISH) HER2 / centromere on chromosome 17 (CEP17) \< 2.0); * ER and PR-negative breast cancer (defined by IHC\<1%); * Measurable metastatic or unresectable disease based on response evaluation criteria in solid tumours (RECIST) 1.1. * Indicated for treatment with either weekly paclitaxel or oral capecitabine, as first or second-line chemotherapy in the metastatic/unresectable setting (as determined by the consenting investigator); * Be willing to provide tissue from a newly obtained core or excisional biopsy of a tumor lesion. Newly-obtained is defined as a specimen obtained during screening. Archival tissue is acceptable if no intervening anti-neoplastic therapy has been administered, and if sufficient material is available for analysis (see section 8.0 for requirements); * Have a performance status of 0 or 1 on the Eastern Cooperative Oncology Group (ECOG) Performance Scale. * Demonstrate adequate organ function as defined by protocol defined lab values * Female subjects of childbearing potential must have a negative urine or serum pregnancy within 72 hours prior to receiving the first dose of study medication. If the urine test is positive or cannot be confirmed as negative, a serum pregnancy test will be requir…