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

This is a Phase III trial where participants will be randomized to two treatment groups, which means participants will be assigned by equal chance to a treatment group. This trial will be double-blinded, which means neither the participants nor the trial doctors will know which of the two treatments the participants actually receive. Participants will receive either the trial drug with chemotherapy or placebo (which looks like the trial drug but does not have any drug in it) with chemotherapy.

Inclusion Criteria: * Are considered ineligible for combination treatment with a monospecific PD(L)1 targeting immunotherapy plus chemotherapy as per their tumor PD-L1 expression status. * Have confirmed locally recurrent inoperable or metastatic TNBC, or estrogen receptor (ER)-low, human epidermal growth factor receptor 2 (HER2)-negative breast cancer (ER and/or progesterone receptor \[PgR\]) 1% to 10%, HER2 immunohistochemistry \[IHC\] 0, 1+, or 2+ with fluorescence in situ hybridization \[FISH\] negative for HER2 gene amplification) documented prior to trial screening as part of standard of care. * Have at least one measurable lesion as the targeted lesion based on RECIST v1.1. * Have provided a tissue sample, archival or fresh, during the screening period (bone biopsies, fine needle aspiration biopsies, and samples from pleural or peritoneal fluid are not acceptable; participants with only one target lesion are not eligible to participate in the trial). * Eastern cooperative oncology group (ECOG) performance status of 0 or 1. Exclusion Criteria: * Have received any of the following therapies or drugs prior to the initiation of trial: * Have received prior systemic anticancer therapy for advanced disease. * Have received prior treatment with a PD(L)-1/vascular endothelial growth factor (VEGF) bispecific antibody. * Have received systemic corticosteroids (at a dosage greater than 10 milligrams \[mg\]/day of prednisone or an equivalent dose of other corticosteroids) within 7 days prior to the initiation of trial treatment. Exception: excluding local, intranasal, intraocular, intra-articular or inhaled corticosteroids, short-term use (\