Endocrine Therapy Fulvestrant & Palbociclib or Aromatase Inhibitor Therapy in Treating Older Patients With Hormone Responsive Breast Cancer That Cannot Be Removed by Surgery

Inclusion Criteria: * Newly diagnosed invasive, estrogen receptor (ER) and/or progesterone receptor (PR)-positive, HER2 negative breast cancer; ER-and/or PR-positive breast cancer is defined by \> 10% staining by immunohistochemistry * Patients must be vulnerable or frail by Balducci Criteria or the patient is refusing breast surgery; vulnerable patients are defined as those with dependence in some instrumental activities of daily living, well controlled co-morbidities, and early symptoms of geriatric syndrome; frail patients are defined as those with three or more co-morbidities, dependence in one or more activities of daily living, or a clinically significant geriatric syndrome; geriatric syndromes include: dementia, delirium, incontinence (fecal and/or urinary), osteoporosis or spontaneous fractures, polypharmacy, visual/hearing impairment, sarcopenia and neglect or abuse * The patient's refusal to proceed with curative breast surgery has to be documented by the surgeon's and medical oncologist's note * Absolute neutrophil count (ANC) \> 1000/uL * Platelets \> 75,000/L * Serum creatinine 1.5 X institutional upper limit of normal (ULN) * Total bilirubin \< 1.5 X ULN * Aspartate aminotransferase (AST)/alanine aminotransferase (ALT) 2.5 ULN * Ability to understand and the willingness to sign a written informed consent document Exclusion Criteria: * Prior aromatase inhibitor therapy * Evidence of distant metastases * Psychiatric illness, which would prevent the patient from…