A Study of Sacituzumab Tirumotecan (Sac-TMT, MK-2870) as Monotherapy and in Combination With Pembrolizumab (MK-3475) in Participants With Triple-Negative Breast Cancer (MK-2870-011/TroFuse-011)

Inclusion Criteria

• Inclusion Criteria: The main inclusion criteria include but are not limited to the following: - Has locally recurrent unresectable or metastatic TNBC that cannot be treated with curative intent - Has not received systemic treatment for locally recurrent unresectable or metastatic breast cancer - Participants previously treated for early-stage breast cancer must have completed all prior therapy for early-stage breast cancer with curative intent at least 6 months before the first disease recurrence - Is a candidate for treatment with pembrolizumab and one of the TPC options: paclitaxel or nab-paclitaxel or gemcitabine + carboplatin - Participants who have AEs due to previous anticancer therapies must have recovered to ≤Grade 1 or baseline with the exception of alopecia or vitiligo. Participants with endocrine-related AEs who are adequately treated with hormone replacement are eligible - Participants who are hepatitis B surface antigen (HBsAg) positive are eligible if they have received hepatitis B virus (HBV) antiviral therapy for at least 4 weeks, and have undetectable HBV viral load - Participants with history of hepatitis C virus (HCV) infection are eligible if HCV viral load is undetectable Exclusion Criteria: The main exclusion criteria include but are not limited to the following: - Has breast cancer amenable to treatment with curative intent - Has TNBC with evaluable tumor programmed death ligand 1 (PD-L1) expression at combined positive score (CPS) ≥10 - Has received prior systemic therapy for treatment of locally recurrent unresectable or metastatic breast cancer - Has Grade ≥2 peripheral neuropathy - Has history of documented severe dry eye syndrome, severe Meibomian gland disease and/or blepharitis, or severe corneal disease that prevents/delays corneal healing - Has active inflammatory bowel disease requiring immunosuppressive medication or previous history of inflammatory bowel disease - Has uncontrolled, significant cardiovascular disease or cerebrovascular disease - Has skin only metastatic disease - Has advanced/metastatic, symptomatic visceral spread at risk of rapidly evolving into life-threatening complications - Human immunodeficiency virus (HIV)-infected participants with a history of Kaposi's sarcoma and/or Multicentric Castleman's Disease - Has known additional malignancy that is progressing or has required active treatment within the past 5 years - Has known active central nervous system (CNS) metastases and/or carcinomatous meningitis. Participants with previously treated brain metastases may participate provided they are radiologically stable - Active autoimmune disease that has required systemic treatment in the past 2 years. Replacement therapy (eg, thyroxine, insulin, or physiologic corticosteroid) is allowed - History of (noninfectious) pneumonitis/interstitial lung disease that required steroids or has current pneumonitis/interstitial lung disease - Concurrent active Hepatitis B (defined as HBsAg positive and/or detectable HBV deoxyribonucleic acid (DNA)) and Hepatitis C virus (HCV) (defined as anti-HCV antibody (Ab) positive and detectable HCV ribonucleic acid (RNA)) infection - History of stem cell/solid organ transplant - Has not adequately recovered from major surgery or has ongoing surgical complications