Patritumab Deruxtecan for Advanced HER2 Positive Breast Cancer

Inclusion Criteria: 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 Part 1 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 Part 1 Arm 2: -Has received no more than 5 prior lines of anti-HER2 therapy in the locally advanced or metastatic setting Part 1 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. Part 2 : Has not received prior systemic therapy (including T-DXd) for recurrent locally advanced or metastatic breast cancer (mBC). Exclusion Criteria: The main exclusion criteria include but are not limited to the following: * Uncontrolled or significant cardiovascular disease * Has any history of (noninfectious) interstitial lung disease (ILD)/ pneumonitis irrespective of steroid use or has current ILD or suspected ILD * Has clinically severe respiratory compromise * Has any history of or evidence of any current leptomeningeal disease * Has clinically significant corneal disease * Evidence of ongoing uncontrolled systemic bacterial, fungal, or viral infection * HIV infected participants with a history of Kaposi's sarcoma and/or Multicentric Castleman's Disease * Known additional malignancy that is progressing or has required active treatment within the past 3 years * Part 1: Evidence of spinal cord compression or brain metastases * Part 2: Evidence of spinal cord compression or brain/CNS metastases. * Has an active infection requiring systemic therapy * Concurrent active HBV and HCV infection * Has had major surgical procedure (excluding placement of vascular access) less than 28 days Part1: Arm 3 ONLY \- Has received prior treatment with tucatinib, lapatinib, or neratinib, or any investigational HER2-targeted tyrosine kinase inhibitors in the locally advanced or metastatic setting