Discontinuation of Maintenance HER-2 Directed Therapy in Long-Term Survivors of Metastatic HER-2 Positive Breast Cancer

Inclusion Criteria: 1. Patients with a diagnosis of HER-2 positive metastatic (Stage IV) breast cancer. 2. Patients in complete radiological remission (CRR), including a stable bone scan, as determined by computed tomography (CT), positron-emission tomography (PET), or PET-CT. a. Patients with brain metastasis are allowed to participate as long as their disease has been treated and radiologically stable for at least 36 months. 3. Patients must be on the same or current anti-HER-2 directed therapy for at least 36 months. 4. Archived tumor biopsy available. 5. Patients with no evidence of circulating tumor deoxyribonucleic acid (ctDNA) as determined by the Signatera assay. 6. Patients willing to stop maintenance anti-HER-2 directed therapy with close monitoring. 7. Patients with an Eastern Cooperative Oncology Group (ECOG) performance score from 0 to 2. 8. Patients ≥ 18 years of age. 9. Ability to understand and the willingness to sign a written informed consent document. Exclusion Criteria: 1. Patients with uncontrolled metastatic disease. 2. Patients whose disease has been controlled for less than 36 months on the same or current anti-HER-2 therapy. 3. Patients who are currently receiving or have received treatment for a secondary cancer other than resected non-melanoma skin cancer lesions or in situ cancer within the past 24 months. 4. Patients positive for ctDNA (which occurs when a patient's blood sample contains ≥2 target markers) with the Signatera assay. 5. Use of investigational drugs ≤ 28 days prior to study enrollment and during the study. 6. History or current evidence of any condition, therapy, or laboratory abnormality that might confound the results of the trial, interfere with the patient's participation for the full duration of the trial, or that makes participation in the trial to be not in the best interest of the patient in the opinion of the Investigator. 7. Patients with impaired decision-making capacity. Patients who are found to be ctDNA+ at study entry will be recorded as a screen failure (Section 5.4). Their Signatera testing results will be provided to their treating physician to aid in clinical decision-making for disease management and treatment.