The goal of this study is to find out if the experimental product, sacituzumab govitecan-hziy (SG) in combination with pembrolizumab given after surgery, is effective and safe compared to the treatment of physician's choice (TPC) which includes either pembrolizumab or pembrolizumab plus capecitabine in participants with triple negative breast cancer that still remains after surgery and pre-surgical treatment.

Key Inclusion Criteria:

• Age > 18 years, with residual invasive triple negative breast cancer (TNBC) in the breast or lymph nodes after neoadjuvant therapy and surgery:

  • TNBC criteria for the study is defined as estrogen receptor (ER) and progesterone receptor (PR) ≤ 10%, human epidermal growth factor receptor 2 (HER2)-negative per American Society of Clinical Oncology and College of American Pathologists (ASCO/CAP) guidelines (immunohistochemistry (IHC) and/or in situ hybridization (ISH)).

• Adequate excision and surgical removal of all clinically evident of disease in the breast and/or lymph nodes and have adequately recovered from surgery.

• Submission of both pre-neoadjuvant treatment diagnostic biopsy and resected residual invasive disease tissue.

• Eastern Cooperative Oncology Group (ECOG) performance status 0-1.

• Individuals must have received appropriate radiotherapy aligned with local/institutional practice and have recovered prior to starting study treatment.

• Adequate organ function.

Key Exclusion Criteria:

• Stage IV (metastatic) breast cancer as well as history of any prior (ipsi- or contralateral) invasive breast cancer.
• Prior treatment with another stimulatory or coinhibitory T-cell receptor agent (eg, cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), OX-40, cluster of differentiation 137 (CD137), prior treatment with any HER2-directed agent, prior endocrine therapy for > 4 weeks or planned concurrent endocrine therapy while receiving on-study treatment.
• Evidence of recurrent disease following preoperative therapy and surgery.
• Prior treatment with topoisomerase 1 inhibitors or antibody-drug conjugates (ADCs) containing a topoisomerase inhibitor.
• Individuals with germline breast cancer gene (BRCA) mutations.
• Myocardial infarction or unstable angina pectoris within 6 months of enrollment or history of serious ventricular arrhythmia (ie, ventricular tachycardia or ventricular fibrillation), high-grade atrioventricular block, or other cardiac arrhythmias or Left ventricular ejection fraction (LVEF) of < 50%
• Active serious infections requiring anti-microbial therapy.

Note: Other protocol defined Inclusion/Exclusion criteria may apply.