PATIENT WEBSITE
PATIENT WEBSITE

DO YOU WANT TO
KNOW MORE ABOUT
ESR1 MUTATIONS AS
A BIOMARKER?

You can find more detailed
information here

What are ESR1 mutations?

ESR1 mutations are
a key biomarker in advanced
or metastatic breast cancer1-8

ESR1 mutations are a major mechanism
of developing acquired resistance
to endocrine therapy1-8

Learn why

Why test?

ESR1 mutations may be found
in ~40% of breast cancer tumours in patients
with a/mBC following ET1,9–11

ESR1 mutations may drive cancer growth,
cause endocrine resistance and lead
to poor outcomes1-5,12

Learn why

When to test?

ESR1 mutation prevalence
in breast tumours changes
over time1,9

Routine testing at each disease progression*
is crucial as ESR1 mutations are rarely
found in the primary tumour1,9,13-18

Learn why

*If not detected previously

How to test?

Liquid biopsy (ctDNA) is
recommended as the preferred
testing methodology14

Given the acquired nature of ESR1 mutations,
archived primary breast cancer tissue should
NOT be used for ESR1 mutation testing17

Learn why

Technical aspects of testing

For optimal testing
a multidisciplinary
workflow should be followed

ESR1 mutations can be detected using
highly sensitive techniques and should be
reported in a timely manner18

Learn why

Headshots are not actual HCPs or patients. For illustrative purposes only.

a/mBC: advanced/metastatic breast cancer; ctDNA: circulating tumour DNA; ER+: oestrogen receptor-positive; ESR1: oestrogen receptor 1; ET: endocrine therapy; FAQs: frequently asked questions; HCP: healthcare professional; HER2-: human epidermal growth factor receptor 2-negative.

1. Brett JO, et al. Breast Cancer Res. 2021;23(1):85. 2. Clatot F, et al. Breast Cancer Research. 2020;22(1):56. 3. Chandarlapaty S, et al. JAMA Oncol. 2016;2(10):1310. 4. Turner NC, et al. Clinical Cancer Research. 2020;26(19):5172–7. 5. Zundelevich A, et al. Breast Cancer Research. 2020;22(1):16. 6. Schiavon G, et al. Sci Transl Med. 2015;7(313):313ra182. 7. Dustin D, et al. Cancer. 2019;125(21):3714-28. 8. Lei JT, et al. J Cancer Metastasis Treat. 2019;5:38. 9. Allouchery V, et al. Breast Cancer Research. 2018;20(1):40. 10. Bhave MA, et al. Breast Cancer Res Treat. 2024;207(3):599-609. 11. Bidard FC, et al. J Clin Oncol. 2022;40(28):3246–56. 12. Liao H, et al. Front Oncol. 2020;10:587671. 13. ESMO Metastatic Breast Cancer Living Guideline, v1.2 April 2025. Accessed March 2026. Available at: https://www.esmo.org/guidelines/living-guidelines/esmo-living-guideline-metastatic-breast-cancer. 14. Burstein HJ, et al. J Clin Oncol. 2023;41(18):3423–5. 15. Lee N, et al. Int J Mol Sci. 2020;21(22):8807. 16. Russano M, et al. J Exp Clin Cancer Res. 2020;39(1):95. 17. Gradishar WJ, et al. J Natl Compr Canc Netw. 2023;21(6):594-608. 18. Najim O, et al. Front Oncol. 2023;13:1221773.