Endocrine Resistance and Biomarker Reassessment in ER-Positive, HER2-Negative Metastatic Breast Cancer

In this segment, Dr. Gregory Vidal explains what it means when endocrine therapy stops working in ER-positive, HER2-negative metastatic breast cancer and why resistance can develop over time. He describes how, although endocrine therapy is highly effective for many patients, cancer cells can adapt and find alternative pathways to continue growing despite treatment. This process, known as endocrine resistance, may occur months or years after initiating therapy. Dr. Vidal emphasizes that disease progression does not mean there are no further options, but rather signals the need to reassess the tumor’s biology. He highlights the importance of repeat biomarker testing at progression, noting that new molecular changes, such as ESR1 mutations, may emerge and guide the selection of subsequent targeted therapies. This segment underscores the dynamic nature of ER-positive, HER2-negative metastatic breast cancer and reinforces the importance of ongoing molecular evaluation to inform the next phase of treatment.