‣ The main inclusion criteria include but are not limited to the following:

⁃ Has histologically confirmed HER2+ locally advanced unresectable breast cancer or metastatic breast cancer

⁃ Human immunodeficiency virus (HIV)-infected participants must have well-controlled HIV on antiretroviral therapy (ART)

⁃ Participants who are hepatitis B surface antigen (HBsAg) positive are eligible if they have received HBV antiviral therapy for at least 4 weeks, and have undetectable hepatitis B virus (HBV) viral load before allocation

⁃ Participants with history of hepatitis C virus (HCV) infection are eligible if HCV viral load is undetectable

⁃ Eastern Cooperative Oncology Group (ECOG) performance status 0 to 1 within 7 days before start of study intervention

‣ Arm 1:

⁃ Has received at least a minimum of 2 and a maximum of 5 prior lines of anti-HER2 therapy in the locally advanced or metastatic setting

⁃ Had disease progression on or after any previous trastuzumab deruxtecan (T-DXd) treatment

‣ Arm 2:

• Has received no more than 5 prior lines of anti-HER2 therapy in the locally advanced or metastatic setting

‣ Arm 3:

• Has received and had disease progression from T-DXd treatment in any setting and a maximum of 3 prior lines of anti-HER2 therapy in the locally advanced or metastatic setting. T-DXd must be the most recent therapy received before enrollment.