Monitoring for Cancer Spread to the Central Nervous System (CNS) in People With Breast Cancer

Inclusion Criteria

• •Patients with Stage IV metastatic HER2+ breast cancer without CNS disease s/p 1 or more lines of HER2 directed therapy (Cohort A Only)
• •Patients with Stage II-III HER2+ breast cancer without CNS disease (Cohort B Only)
• •Male and Female participants Age ≥18 years
• •HER2+ as defined by ASCO/CAP guidelines\*
• •Ability to undergo bedside Lumbar puncture to obtain cerebrospinal fluid; if beside LP is not successful due to patient discomfort or inability to obtain spinal fluid then patients will be offered LP through interventional radiology and patients will continue to be monitored on study
• •Able to provide written informed consent \*ASCO/CAP guidelines: HER2+ defined as IHC 3+ positive and/or by ISH average copy number ≥ 6 signals/cell