Pre-Operative Window of Adjuvant Endocrine Therapy to Inform RT Decisions in Older Women With Early-Stage Breast Cancer

This single arm pilot study evaluates the use of pre-operative endocrine therapy in women with early stage ER+ breast cancer who are 65 years or older and are scheduled to have breast conservation surgery (BCS). The purpose of this study is to see if tolerance of pre-operative endocrine therapy helps inform decisions on whether or not to omit radiation. Participants will be treated with the novel approach of 3 months of pre-operative endocrine therapy, so that the participants and providers will have some indication of tolerance prior to making a decision about radiation omission. Tolerance of the endocrine therapy will be assessed by patient reported outcome (PRO) measures during neoadjuvant and adjuvant endocrine therapy treatment periods. Breast cancer participants and their surgical oncologists will be asked their preference regarding radiation therapy before starting endocrine therapy and again pre-operatively. They will make a determination regarding radiation therapy as per standard care. The hypothesis is that knowledge of tolerance of endocrine therapy will influence the decision by the patient and the surgical oncologist whether or not to elect radiation omission.