Study of Olaparib Plus Pembrolizumab Versus Chemotherapy Plus Pembrolizumab After Induction With First-Line Chemotherapy Plus Pembrolizumab in Triple Negative Breast Cancer (TNBC) (MK-7339-009/KEYLYNK-009)

Inclusion Criteria

Induction Period:

• Has locally recurrent inoperable TNBC that has not previously been treated with chemotherapy and that cannot be treated with curative intent OR has metastatic TNBC that has not been previously treated with chemotherapy
• Has been treated with anthracycline and/or a taxane in the neoadjuvant/adjuvant setting, if they received systemic treatment in the neoadjuvant/adjuvant setting, unless anthracycline and/or taxane was contraindicated or not considered the best treatment option for the participant in the opinion of the treating physician
• Has measurable disease based on RECIST 1.1
• Has provided a recently obtained or archival (no more than 3 years old) core or excisional biopsy of a tumor lesion not previously irradiated
• Has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 as assessed within 7 days prior to the start of induction study treatment
• Has a life expectancy ≥27 weeks from the day of first study treatment
• Demonstrate adequate organ function within 10 days prior to the start of study treatment
• A male participant must agree to be abstinent or use contraception and refrain from donating sperm during the intervention period and for at least the time needed to eliminate each study intervention (95 days for olaparib and chemotherapy; no requirement for pembrolizumab)
• A female participant must not be pregnant or breastfeeding and must agree to the following if is a woman of childbearing potential (WOCBP): have a negative pregnancy test within 24 hours before the start of study treatment and agree to be abstinent or use contraception and refrain from donating eggs (ova, oocytes) during the intervention period and for at least the time needed to eliminate each study intervention (180 days for olaparib and chemotherapy; 120 days for pembrolizumab)

Post-induction Period:

• Has received up to 6 cycles but not less than 4 cycles of induction therapy without permanently discontinuing from pembrolizumab or both carboplatin and gemcitabine
• Has achieved complete response (CR), partial response (PR), or stable disease (SD) based on RECIST 1.1 by Blinded Independent Central Review (BICR) at the Week 18 evaluation
• Is able to complete during post-induction at least the Cycle 1, Day 1 doses of olaparib and pembrolizumab or the Cycle 1, Day 1 doses of at least one of the chemotherapy agents being administered at the end of induction (carboplatin and/or gemcitabine) in addition to pembrolizumab
• Has ECOG performance status of 0 or 1, as assessed within 7 days prior to the start of post-induction study treatment
• Has no higher than Grade 1 toxicities related to induction therapy (excluding alopecia) prior to randomization

Exclusion Criteria

Induction Period:

• Has a known additional malignancy that is progressing or has required active treatment within the past 5 years with the exception of basal cell carcinoma of the skin, squamous cell carcinoma of the skin, or carcinoma in situ (eg, cervical cancer in situ) that have undergone potentially curative therapy
• Has a diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy (in dosing exceeding 10 mg daily of prednisone equivalent) or any other form of immunosuppressive therapy within 7 days prior the first dose of study treatment
• Has an active autoimmune disease that has required systemic treatment in the past 2 years
• Has known active central nervous system (CNS) metastases and/or carcinomatous meningitis
• Has myelodysplastic syndrome (MDS)/acute myeloid leukemia (AML) or has features suggestive of MDS/AML
• Has a history of (non-infectious) pneumonitis\interstitial lung disease that required steroids or current pneumonitis\interstitial lung disease
• Has active, or a history of, interstitial lung disease
• Has a known history of active tuberculosis
• Has an active infection requiring systemic therapy
• Has a known history of human immunodeficiency virus (HIV) infection
• Has a