ROSETTA Breast-01: The Effects and Safety of Pumitamig in Patients With Triple-Negative Breast Cancer

The study consists of a: 1. Screening period (up to 28 days); 2. Treatment period, during which participants will receive pumitamig or placebo in combination with chemotherapy (until disease progression, the occurrence of intolerable toxicity, withdrawal, death, or trial termination \[whichever comes first\]); 3. Safety follow-up (FU) period (for up to 90 days after administration of the last dose of trial treatment) and survival follow-up (until the participant dies, withdraws consent for survival status follow-up, loss of contact, or sponsor decision, whichever occurs first). Participants will be randomized 1:1 to receive either pumitamig in combination with the treatment of physician's choice (TPC) chemotherapy (Arm 1) or placebo in combination with TPC chemotherapy (Arm 2). Chemotherapy will be administered per standard of care. The randomization will be stratified based on the following factors: * Prior treatment with cancer immunotherapy (yes versus no) * On-trial chemotherapy regimen (paclitaxel/nab-paclitaxel versus gemcitabine plus carboplatin versus eribulin) * Geography (East Asia versus the rest of the world \[ROW\]) * PD-L1 status (combined positive score \[CPS\] less than \[\<\] 1 versus 1 less than or equal to \[\<=\] CPS \<10).