⁃ 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