Genetic Analysis in Blood and Tumor Samples From Patients With Advanced or Metastatic Estrogen Receptor Positive and HER2 Negative Breast Cancer Receiving Palbociclib and Endocrine Therapy

Inclusion Criteria: PRE-REGISTRATION INCLUSION CRITERIA * Women who have disease that is amenable to biopsy and agree to undergo a standard of care and /or research biopsy * Note: If a standard of care biopsy was recently obtained =\< 2 months of pre-registration, eligible patients should agree to a research biopsy of recurrent or metastatic breast cancer prior to the start of protocol treatment to collect additional core samples for research purposes * Patients must satisfy one of the following criteria for prior therapy: * First line setting: No prior endocrine therapy in the metastatic setting with no more than one prior line of chemotherapy in the advanced/metastatic setting * Second line setting: Progression on one prior line of endocrine based therapy monotherapy either in the adjuvant or advanced/metastatic setting; either one or two prior lines of chemotherapy in the advanced setting are allowed * Note: Patients receiving bisphosphonate or denosumab therapy prior to registration may continue at the same intervals used prior to study registration * First line therapy setting only: The intention to begin palbociclib and letrozole as treatment for locally advanced or metastatic breast cancer * Second line therapy setting only: The intention to begin palbociclib and fulvestrant as treatment for metastatic breast cancer (after progression on first line endocrine therapy) * Note: Patients who are to receive second line endocrine therapy are allowed to remain …