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How to test
for ESR1m
Importance of
ESR1m detection
Hear from
the Experts

In ER+/HER2- mBC,

ESR1m are detected and actionable at progression.1

Test for ESR1m at every progression to identify what’s driving your patient’s disease1,2

Recommendations for testing

  • Use liquid biopsy to test for ESR1 mutations at progression on ET3,4
  • Blood-based ctDNA testing (via liquid biopsy) is considered the preferred testing method for acquired mutations due to greater sensitivity3,5
  • Archival tissue samples are not recommended for detecting ESR1 mutations6

    – Due to their acquisition following 1L ET + CDK4/6i, ESR1 mutations are rarely found in primary tumors1

  • ctDNA can provide a real-time tumor biomarker profile through liquid biopsy4,7

NCCN makes no warranties of any kind whatsoever regarding their content, use or application and disclaims any responsibility for their application or use in any way. Refer to NCCN Guidelines for full recommendations.

Abbreviations: 1L, 1st Line; CDK4/6i, cyclin-dependent kinase 4/6 inhibitor; ctDNA, circulating tumor DNA; ER+, estrogen receptor-positive; ESR1, estrogen receptor 1; ESR1m, estrogen receptor 1 mutation; ET, endocrine therapy; HER2-, human epidermal growth factor receptor 2-negative; mBC, metastatic breast cancer; NCCN, National Comprehensive Cancer Network® (NCCN®); PCR, polymerase chain reaction.

References: 1. Brett JO, Spring LM, Bardia A, Wander SA. ESR1 mutation as an emerging clinical biomarker in metastatic hormone receptor-positive breast cancer. Breast Cancer Res. 2021;23(1):85. 2. Zhang K, Hong R, Xu F, et al. Clinical value of circulating ESR1 mutations for patients with metastatic breast cancer: a meta-analysis. Cancer Manag Res. 2018;10:2573-2580. 3. Burstein HJ, DeMichele A, Somerfield MR, et al. Biomarker Testing and Endocrine and Targeted Therapy in Metastatic Breast Cancer Expert Panels. Testing for ESR1 mutations to guide therapy for hormone receptor-positive, human epidermal growth factor receptor 2-negative metastatic breast cancer: ASCO guideline rapid recommendation update. J Clin Oncol. 2023;41(18):3423-3425. 4. Russano M, Napolitano A, Ribelli G, et al. Liquid biopsy and tumor heterogeneity in metastatic solid tumors: the potentiality of blood samples. J Exp Clin Cancer Res. 2020;39(1):95. 5. Dustin D, Gu G, Fuqua SAW. ESR1 mutations in breast cancer. Cancer. 2019;125(21):3714-3728. 6. Spoerke JM, Gendreau S, Walter K, et al. Heterogeneity and clinical significance of ESR1 mutations in ER-positive metastatic breast cancer patients receiving fulvestrant. Nat Commun. 2016;7:11579. 7. Lee N, Park MJ, Song W, et al. Currently applied molecular assays for identifying ESR1 mutations in patients with advanced breast cancer. Int J Mol Sci. 2020;21(22):8807. 8. Referenced with permission from the NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines®) for Breast Cancer V.4.2025. © National Comprehensive Cancer Network, Inc. 2025. All rights reserved. Accessed July 08, 2025. To view the most recent and complete version of the guideline, go online to NCCN.org. 9. Gradishar WJ, Moran MS, Abraham J, et al. NCCN Guidelines® Insights: Breast Cancer, Version 4.2023. J Natl Compr Canc Netw. 2023;21(6):594-608.