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) \>= 1500/mm\^3 (1.5 x 10\^9/L)
* Platelet count \>= 100,000/mm\^3 (100 x 10\^9/L)
* Creatinine clearance \>= 30 ml/min calculated using the Cockcroft-Gault formula
* Total serum bilirubin =\< 1.5 upper limit of normal (ULN) (\< 3 ULN if Gilbert's disease)
* Aspartate aminotransferase (AST) and/or alanine aminotransferase (ALT) =\< 3 x ULN (=\< 5.0 x ULN if liver metastases present)
* Alkaline phosphatase =\< 2.5 x ULN (=\< 5 x ULN if bone or liver metastases present)