Defining Endocrine Resistance in PIK3CA-Mutated HR+/HER2-Negative Advanced Breast Cancer

Dr. Jason Mouabbi introduces the discussion on managing PIK3CA-mutated HR-positive/HER2-negative advanced breast cancer in clinical practice, with a focus on treatment selection and practical adverse-event management. He begins by reviewing the distinction between primary and secondary endocrine resistance and explains how the timing of disease recurrence or progression helps define these clinical states. Dr. Mouabbi discusses why distinguishing endocrine resistance subtypes is important when considering subsequent treatment strategies and the potential role of targeted therapies. He highlights actionable alterations that may inform treatment selection in HR-positive/HER2-negative advanced breast cancer, including PIK3CA, ESR1, AKT1, PTEN, and HER2 alterations. The discussion emphasizes the importance of identifying targetable molecular changes in patients with endocrine-resistant disease and considering how these findings may support continued use of endocrine-based treatment approaches.