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.
Uncertainty over optimal testing parameters, however, produces inconsistent testing practices. It also creates coverage friction across medical and pharmacy benefits and delays care, according to the report, titled "Managed Care Approaches to ESR1-Mutated Advanced Breast Cancer."
AMCP urges payers to align benefits and streamline prior authorization
AMCP's recommendations for payers include:
- Implementing flexible, evidence-based treatment pathways.
- Aligning coverage policies across medical and pharmacy benefits.
- Streamlining prior authorization through auto-approvals for guideline-concordant testing, extended authorization durations and gold carding.
Payers also stressed the need for total cost-of-care analyses that account for delayed progression rather than testing costs alone. They called for better support for community oncologists and for patient shared decision-making.
Next-generation SERDs raise the stakes for testing consistency
Next-generation selective estrogen receptor degraders are moving into earlier treatment lines. AMCP says that makes testing consistency and multi-stakeholder alignment a critical opportunity to improve patient outcomes.
The program was independently conducted with funding support from AstraZeneca. The peer-reviewed Market Insight supplement appears in the October 2026 edition of the Journal of Managed Care & Specialty Pharmacy.