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: 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 receiv…