AMCP: ESR1 Testing Gaps Create Payer Friction in Breast Cancer Care
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Washington – October 16, 2026 -- Nearly half of patients with hormone receptor positive, HER2 negative advanced breast cancer develop resistance to first-line endocrine therapy driven by the ESR1 mutation (ESR1m), according to a new Academy of Managed Care Pharmacy (AMCP) Market Insights Program report. The report finds that biomarker testing and treatment paradigms are evolving faster than the evidence payers need to manage them.
Testing uncertainty drives inconsistent practice and coverage friction
Patients with ESR1m stay on ineffective treatment until radiologic progression is detected. Monitoring for the mutation with circulating tumor DNA (ctDNA) liquid biopsy before progression can enable an early switch to effective therapy and extend time on first-line treatment.