Receptor Status Changes, HER2-Low Discordance, and TNBC Transformation in Metastatic Breast Cancer: Prognostic Significance and Impact on Survival Outcomes

Background/Objectives: Therapeutic options for metastatic breast cancer vary according to hormone receptor (HR) status, human epidermal growth factor receptor 2 (HER2) status, and, importantly, the newly recognized HER2-low status. In triple-negative breast cancer (TNBC), characterized by the absence of HR and HER2 receptors, therapeutic approaches and survival rates differ significantly. Current treatments have improved survival rates in metastatic diseases, resulting in an increased demand for secondary biopsies. The findings from these biopsies affect the range of therapeutic options.