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

PRIMARY OBJECTIVES: I. To determine treatment failure-free survival (TFFS) rate at one year of combination therapy with pure estrogen antagonist, fulvestrant and cyclin-dependent kinase (CDK) inhibitor, palbociclib as primary endocrine therapy in patients 70 years or older with newly diagnosed non-metastatic hormone receptor positive, human epidermal growth factor receptor 2 (HER-2) negative breast cancer. SECONDARY OBJECTIVES: I. To determine 1- and 2-year progression free survival. II. To determine safety and toxicity of this combination in the population of patients 70 years or older. III. To determine whether longitudinal changes in geriatric assessment measures correlate with tolerability of this regimen. OUTLINE: Patients receive fulvestrant intramuscularly (IM) on days 1 and 15. Patients also receive palbociclib orally (PO) once daily (QD) on days 1-21. Courses repeat every 28 days in the absence of disease progression or unacceptable toxicity. After completion of study treatment, patients are followed up for 12 weeks.