A Phase 1b/2, Multicenter, Open-label, Dose Regimen Determination and Dose Expansion Trial to Evaluate the Safety, Tolerability, Anti-tumor Activity, and an Optimal Dose Regimen of Patritumab Deruxtecan (HER3-DXd) With Trastuzumab Deruxtecan (T-DXd) in Participants With Hormone Receptor Positive, HER2-low or HER2-ultralow, Unresectable or Metastatic Breast Cancer (HERTHENA-Breast02)

Key Inclusion Criteria: 1. Pathologically documented breast cancer that meets the following: 1. Unresectable or metastatic. 2. HR+ based on testing performed locally. HR+ (estrogen receptor \[ER\] and/or progesterone receptor \[PgR\] positive \[ER or PgR greater than equal to (≥)1 percent (%)\] per American Society of Clinical Oncology \[ASCO\]/College of American Pathologists \[CAP\] 2020 guidelines) in the unresectable or metastatic setting. 3. Assessed as HER2-low (defined as Immunohistochemistry (IHC)2+/In-situ hybridization (ISH)- or IHC1+) or HER2-ultralow (defined as IHC 0 wi…