Moderator: SABCS Co-director and AACR Past-president Carlos L. Arteaga, MD, director of the Breast Cancer Program at Vanderbilt-Ingram Cancer Center Analysis of Blood Samples Finds ESR1 Gene Mutations Are Prevalent and Associated With Worse Overall Survival; Breast-conserving Therapy Yielded Better Outcomes Than Mastectomy For Early-stage Patients; Mastectomy Plus Reconstruction has Higher Complication Rates and Costs Than Lumpectomy Plus Radiation; and Resistance of ER-positive Breast Cancer to Tamoxifen Therapy May be Driven by APOBEC3B.