Anastrozole, Palbociclib, Trastuzumab and Pertuzumab in HR-positive, HER2-positive Metastatic Breast

Inclusion Criteria: * Women or men with metastatic breast cancer, measurable or evaluable disease including bone metastasis only (as per the Response Evaluation Criteria in Solid Tumors \[RECIST\] v1.1) * No prior systemic treatment for metastatic breast cancer * Pathologic confirmation of metastatic breast cancer diagnosed by core needle biopsy * Metastatic breast cancer with any evidence of ER or PR positivity in ≥ 1% cells in biopsy specimens from either a primary or metastatic site * Evidence of HER2 positive metastatic breast cancer in either a primary or metastatic site, if 3+ by an IHC method defined as uniform membrane staining for HER2 in 10% or more of tumor cells or demonstrate HER2 gene amplification by an ISH method (single probe, average HER2 copy number ≥6.0 signals/cell; dual probe HER2/CEP17 ratio ≥2.0 with an average HER2 copy number ≥4.0 signals/cell; dual probe HER2/chromosome enumeration probe (CEP) 17 ratio ≥2.0 with an average HER2 cop number \<4.0 signals/cell; and HER2/CEP17 ratio \<2.0 with an average HER2 copy number ≥6.0 signals/cell) or amplified by FISH \> 2.0. High average copy number of HER2 (≥6.0 signals/cell) is considered positive regardless of the HER2/CEP17 ratio. * Women or men 18 years and older * Eastern Cooperative Oncology Group (ECOG) performance status (PS) 0-2 * Stable brain metastasis allowed (\>2 weeks, clinically stable post treatment with surgery +/- radiation or radiation alone and off steroids) * Transthoracic echocardiogram…