# Switching to camizestrant at ESR1 mutation emergence before disease progression during first-line treatment of hormone receptor-positive advanced breast cancer (SERENA-6): extended analysis of a double-blind, placebo-controlled, randomised, phase 3 trial

Source: https://onco.cc/key-papers/paper-turner-serena-6-extended-lancet-oncol-2026/  
OnCo record `paper-turner-serena-6-extended-lancet-oncol-2026` (Key paper). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

With longer follow-up, switching to camizestrant when an ESR1 mutation appeared in the blood kept its benefit and also lengthened control on the next treatment.

## Summary

SERENA-6 tested ctDNA for ESR1 mutation every two to three months with Guardant360 CDx in patients on first-line aromatase inhibitor plus CDK4/6 inhibitor at 264 centres in 23 countries. From June 2021 to June 2024, 3,325 patients were screened, 3,256 had at least one test and 548 had a positive ESR1 test by screening closure; 315 were randomised to switch to camizestrant with the CDK4/6 inhibitor (157) or continue the aromatase inhibitor (158). At a median follow-up of 23.5 months, median progression-free survival was 16.8 months (95% CI 14.7 to 19.4) against 9.2 months (7.2 to 9.7), hazard ratio 0.45 (0.34 to 0.59), descriptive and consistent with the interim analysis. Median second progression-free survival was 25.7 months (20.4 to 30.3) against 19.1 months (16.8 to 21.0), hazard ratio 0.63 (0.46 to 0.86), p = 0.0037.

## Fields

- Kind: Key paper
- Last checked: 2026-11-04
- Journal: The Lancet Oncology
- Year: 2026
- DOI: 10.1016/S1470-2045(26)00287-1
- Authors: Turner NC, Mayer EL, Park YH, et al.
- Findings: 3,256 tested; 548 ESR1-positive; 315 randomised.; Updated PFS 16.8 vs 9.2 months, HR 0.45 (0.34 to 0.59).; Second PFS 25.7 vs 19.1 months, HR 0.63 (0.46 to 0.86), p = 0.0037.
- What it means: Acting on a resistant subclone found in blood keeps its benefit into the next line of treatment. It works where the clone carries a mutation that both marks it and chooses the drug.
- Caveats: Advanced disease, hotspot genotyping rather than residual disease testing.; Overall survival not reported in this analysis.

## Sources

- Turner et al., Lancet Oncol 2026 (SERENA-6 extended analysis): https://doi.org/10.1016/S1470-2045(26)00287-1
- PubMed: https://pubmed.ncbi.nlm.nih.gov/42442380/

## Connected records

- cancers: [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/)
- fronts: [Diagnostics & Biomarkers](https://onco.cc/fronts/diagnostics/)
- technologies: [Liquid biopsy (ctDNA)](https://onco.cc/technologies/liquid-biopsy/)
- targets: [Estrogen receptor (ERα)](https://onco.cc/targets/estrogen-receptor/)
- drugs: [Camizestrant](https://onco.cc/drugs/camizestrant/), [Guardant360 CDx](https://onco.cc/drugs/guardant360-cdx/)
- companies: [AstraZeneca](https://onco.cc/companies/astrazeneca/)
- terms: [Circulating tumour DNA (ctDNA)](https://onco.cc/terms/ctdna/), [ESR1 mutation](https://onco.cc/terms/esr1-mutation/)
- trials: [SERENA-6](https://onco.cc/trials/serena-6/)
- journals: [The Lancet Oncology](https://onco.cc/journals/lancet-oncology/)
- biomarkers: [ESR1 mutation (ligand-binding domain, usually in ctDNA)](https://onco.cc/biomarkers/esr1-mutation-ctdna/)

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