Abstract
A mutation in the estrogen receptor alpha gene (ESR1m) following first-line treatment with endocrine therapy in hormone receptor-positive metastatic breast cancer occurs in nearly half of patients. Detection of this mutation prior to radiologic progression using circulating tumor DNA (ctDNA)-based monitoring is an emerging practice that may allow an early switch to a more effective therapy. To discuss approaches to managing ESR1m advanced breast cancer (aBC) including ctDNA-based monitoring, AMCP Market Insights virtually convened an expert panel of managed care stakeholders in February 2026. This article provides a qualitative summary of the panel discussion along with key insights and suggested payer practices meant to support informed coverage decisions and guide future work. Key insights include that community oncologists and patients may benefit from support, for example, with treatment pathways and patient navigators. Additionally, patients care about survival outcomes when combined with sustained quality of life and want monitoring practices that take patient-specific considerations into account. A primary consideration of payers related to aBC is that the optimal biomarker testing parameters, including ctDNA-based monitoring for ESR1m aBC, are uncertain, which leads to inconsistent testing practices and the need for management that promotes consistency while mitigating delays in care. Payers acknowledge that the role of next-generation selective estrogen receptor degraders is evolving based on current data and ongoing clinical trials. Suggested payer practices involve care delivery, coverage, and system advancements including engaging in multistakeholder conversations and advocating for or participating in evidence generation.