ESR1 mutations are rarely found in primary tumors but develop in metastatic settings under pressure from aromatase inhibitors, conferring resistance. This evolution necessitates serial, plasma-based genotyping upon each disease progression to identify these actionable mutations as they emerge.
The success of oral SERD clinical trials hinges on study design. Trials like AMIRA-3 and Axilera failed in their overall populations but showed benefit in ESR1-mutant subgroups. EMERALD succeeded by making this subgroup a co-primary endpoint, proving the importance of targeting the right population from the outset.
A simple clinical biomarker—having received a prior CDK4/6 inhibitor for over 12 months—identifies patients likely to achieve significant progression-free survival (nearly nine months) with single-agent elacestrant. This allows clinicians to select patients for monotherapy without complex genomic profiling.
Post-approval, real-world analyses have validated the efficacy of elacestrant seen in the pivotal EMERALD trial. This confirmation shows that the clinically meaningful progression-free survival of 6-8 months is achievable in routine clinical practice, boosting clinician confidence.
With multiple FDA-approved oral SERDs available, clinical decision-making is heavily influenced by their distinct side effect profiles. Elacestrant predominantly causes nausea, while iminoralestrant causes diarrhea. This distinction is a primary factor in tailoring treatment to individual patients.
The SERINA-6 trial supports a paradigm shift: proactively screening for ESR1 mutations via blood test and switching to camisestrant upon detection, even without radiological progression. This early switch based on molecular signals nearly doubled median progression-free survival from 9 to 16 months.