ER+/HER2- metastatic breast cancer: ESMO Breast Cancer 2026 Satellite Symposium highlights

In this conference update video, Prof. Nadia Harbeck, Dr Tiffany Traina, and Prof. Frederik Marmé share key insights from the ESMO Breast Cancer 2026 Satellite Symposium, sponsored by Menarini Stemline. 

The faculty discusses 2nd line+ treatment strategies and sequencing following endocrine therapy (ET) + CDK4/6i in endocrine therapy–eligible patients with ER+/HER2- metastatic breast cancer (mBC).  

Topics include:  

• Overview of the current ESMO guidelines  
• Intrinsic and acquired endocrine resistance after 1st line ET + CDK4/6i  
• Role of biomarker-selected endocrine-based therapies and key clinical trial data  
• Clinical relevance of ESR1 mutations and testing strategies 

Clinical takeaways

• 2nd line treatment choices are defined by eligibility to receive ET and are driven by biomarker status. For patients whose tumors retained endocrine-sensitivity, guidelines recommend exhausting sequential ET-based regimens 
• Real-world evidence for elacestrant shows a consistent benefit, with ~8–11 months TTNT, aligning with the 8.6-month mPFS observed in patients with longer prior ET + CDK4/6i exposure in the EMERALD subgroup analysis
• In tumors retaining endocrine sensitivity and coexisting PIK3CA and ESR1 mutations, elacestrant monotherapy can be a good option before PI3K/AKTi combination regimens, as data show similar efficacy with a manageable safety profile 
• ESR1-mut testing should be repeated at each progression on ET if previously negative, as detection rates increase over time. Blood-based ctDNA is the preferred method, while archival primary tumor tissue should be avoided, as ESR1-mut typically develop during metastatic treatment