Thie purpose of this study is to find out whether a personalized treatment approach-using a series of ctDNA tests along with standard imaging scans to help decide when to step up (escalate) or decrease (de-escalate) sequential treatments (given one after another)-combined with local therapies (which treat cancer in a specific part of the body) and treatments that prevent cancer from spreading to the central nervous system (CNS; including the brain and spinal cord) can result in long-lasting remission and possibly cure some participants with HER2+ metastatic breast cancer.
Male or female participants who are ≥18 years old with histologically confirmed diagnosis of unresectable locally advanced or MBC.
Stage IV at the diagnosis (i.e., de novo metastatic) as per AJCC 8.
HER2 IHC results of 3+.
Life expectancy of ≥12 weeks.
Patients diagnosed with HER2+ breast cancer as per American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guidelines with HER2 IHC results of 1-2+ and positive FISH or ISH
Prior exposure to anti-HER2 therapy of any kind or any systemic anti-cancer treatment of any kind for breast cancer.
Is currently participating in or has participated in a study of an investigational agent or has used an investigational device within 2 weeks prior to the first dose of study intervention.
Has a diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy (in doses >10 mg daily of oral prednisone equivalent) or any other form of immunosuppressive therapy within 7 days prior to the first dose of study drug. Inhaled, intranasal, intra-articular, or topical steroid use are allowed.