Three important studies have shaped the creation of guidelines for the management of the axilla in hormone receptor-positive/HER2 negative tumors after chemotherapy: The Treatment for Positive Node, Endocrine Responsive Breast Cancer (RxPONDER) trial, the ACOSOG Z0011 trial, and the After Mapping of the Axilla: Radiotherapy or Surgery (AMAROS) trial. This evidence concerns the gene ERBB2 and breast cancer.