Endocrine Treatment Alone as Primary Treatment for Elderly Patients With Estrogen Receptor Positive Operable Breast Cancer and Low Recurrence Score

Inclusion Criteria: * Newly diagnosed histologically or cytologically confirmed operable invasive breast cancer defined as cT1 or T2, N0-1, and M0. * Disease must be ER+ and HER2-. * Ki67 score/proliferative index ≤ 30% or low to intermediate mitotic index * Measurable disease defined as lesions that can be accurately measured in at least one dimension (longest diameter to be recorded) by ultrasound or mammogram. * 70 years of age or older. * ECOG performance status ≤ 3 * Able to understand and willing to sign an IRB approved written informed consent document (or that of legally authorized representative, if applicable). Exclusion Criteria: * Prior surgery for this cancer * A history of other malignancy ≤ 5 years previous which would preclude endocrine treatment of their cancer. * Currently receiving any other investigational agents. * A history of allergic reactions attributed to compounds of similar chemical or biologic composition to any of the agents used in the study. * Uncontrolled intercurrent illness as determined by their treating physician which would limit compliance with study requirements. * Known HIV-positivity on combination antiretroviral therapy because of the potential for pharmacokinetic interactions with endocrine therapies. Appropriate studies will be undertaken in patients receiving combination antiretroviral therapy when indicated.