Palbociclib and Letrozole or Fulvestrant in Treating Patients With Estrogen Receptor Positive, HER2 Negative Metastatic Breast Cancer

Inclusion Criteria: * Documentation of disease: estrogen receptor positive and/or progesterone receptor (PR) positive, HER2 negative metastatic breast cancer; histologic confirmation is required * Measurable disease or non-measurable disease * Planning to begin palbociclib for metastatic disease; one prior line of endocrine therapy and/or chemotherapy for metastatic disease is allowed; patients may begin or have already begun endocrine therapy before they start palbociclib treatment, but no more than two weeks prior to registration * No prior therapy with a CDK inhibitor * Resolution of all acute toxic effects of prior therapy or surgical procedures to CTCAE grade =\< 1 (except alopecia) or to baseline toxicities prior to previous therapy or surgical procedures, prior to registration * No untreated brain metastases; patients with treated brain metastases must have completed treatment with steroids to be eligible * No known interstitial lung disease * No second malignancies other than non-melanoma skin cancers or cervical carcinoma in situ; however, patients are not considered to have a "currently active" malignancy if they have completed therapy and are free of disease for \>= 3 years * No active infection requiring treatment with antibiotics * Patients must be able to swallow and retain oral medication * Eastern Cooperative Oncology Group (ECOG) performance status 0, 1 or 2 * Patients must be able to read and comprehend English or Spanish * Absolute neutrophil count (ANC) \…