Barbara Pistilli, MD, chair of the breast cancer unit, Gustave Roussy, Villejuif, France, provides a case-based discussion of therapeutic options for a patient with pretreated HR+/HER2- (IHC 0) metastatic breast cancer who has developed endocrine resistance.  Dr Pistilli discusses the mechanism of action of antibody-drug conjugates, currently available antibody-drug conjugates for HR+/HER2- metastatic breast cancer, and strategies for managing adverse events associated with antibody-drug conjugates.