Guardant360 CDx Receives European Approval as Companion Diagnostic for Camizestrant in ESR1-Mutated Advanced Breast Cancer

Guardant360 CDx has received CE marking under the European Union’s In Vitro Diagnostic Medical Devices Regulation as a companion diagnostic to identify patients with estrogen receptor (ER)–positive, HER2-negative locally advanced or metastatic breast cancer who may benefit from camizestrant (Etcamah).¹

The blood-based test detects ESR1 mutations in tumor-derived DNA, which allows testing to occur before disease progression. The European decision follows companion diagnostic approvals for the assay and camizestrant in the United States and Japan.

“Guardant360 CDx offers molecular insights that can support informed treatment decisions for patients,” Helmy Eltoukhy, chairman and co-chief executive officer of Guardant Health, stated in a news release. ““What is even more exciting is that we see tremendous potential for this type of testing protocol to transform the [management] of other cancer types to change the future of oncology.”

What is the approved indication for camizestrant in the EU?

In July 2026, the European Commission approved camizestrant in combination with a CDK4/6 inhibitor—palbociclib (Ibrance), ribociclib (Kisqali), or abemaciclib (Verzenio)—for the treatment of adult patients with ER-positive, HER2-negative locally advanced or metastatic breast cancer with a detectable ESR1 mutation and no disease progression during first-line endocrine therapy plus a CDK4/6 inhibitor.²

What data from SERENA-6 supported the European approval of camizestrant for breast cancer?

The approval was based on data from the phase 3 SERENA-6 trial (NCT04964934), a global, double-blind study of 315 adult patients receiving first-line aromatase inhibitor therapy plus a CDK4/6 inhibitor.³ Circulating tumor DNA (ctDNA) was assessed at routine scans every 2 to 3 months; patients with an emergent ESR1 mutation and no radiographic progression were randomly assigned to switch to camizestrant at 75 mg daily or to continue the aromatase inhibitor, keeping the same CDK4/6 inhibitor. Investigator-assessed progression-free survival (PFS) was the primary end point, and overall survival (OS) and PFS after the next line of therapy (PFS2) were secondary end points.

The median PFS was 16.0 months (95% CI, 12.7-18.2) with camizestrant (n = 157) vs 9.2 months (95% CI, 7.2-9.5) with continued aromatase inhibition (n = 158; HR, 0.44; 95% CI, 0.31-0.60; P < .0001). An updated analysis reported a median PFS of 16.6 months (95% CI, 14.7-19.4) vs 9.2 months (95% CI, 7.2-9.7), respectively (HR, 0.46; 95% CI, 0.34-0.62; P < .00001) and showed that ctDNA clearance occurred in 51.0% of evaluable patients receiving camizestrant (n = 98) vs 1.9% of those continuing the aromatase inhibitor (n = 108).⁴ These clearance rates correlated with the OS benefit seen with camizestrant (HR, 0.39; 95% CI, 0.19-0.73).

How have PFS2 and OS findings shaped regulatory review of camizestrant for breast cancer?

At a later preplanned analysis presented at the 2026 ASCO Annual Meeting, the median PFS2 was 25.7 months (95% CI, 20.4-30.3) with camizestrant vs 19.1 months (95% CI, 16.8-21.0) with continued aromatase inhibition (HR, 0.63; 95% CI, 0.46-0.86; P = .00373).⁵ The OS data were immature across the 3 reported data cutoffs, and at the most recent data cutoff, the HR was 0.87 (95% CI, 0.57-1.30).

In the United States (US), the FDA’s Oncologic Drugs Advisory Committee voted 6 to 3 in April 2026 that the SERENA-6 trial had not demonstrated a clinically meaningful benefit of the ctDNA-triggered switch strategy.⁶ On September 4, 2026, the FDA subsequently granted accelerated approval to camizestrant in combination with a CDK4/6 inhibitor for the treatment of adult patients with hormone receptor–positive, HER2-negative locally advanced or metastatic breast cancer that acquires an ESR1 mutation during aromatase inhibitor and CDK4/6 inhibitor therapy, as identified by an FDA-approved test.⁷ The Guardant360 CDx assay is also the companion diagnostic named for the US indication.

References

1. Guardant Health announces approval in Europe of Guardant360 CDx as companion diagnostic for AstraZeneca’s Etcamah (camizestrant) in advanced ER-positive breast cancer. News release. Guardant Health, Inc. October 8, 2026. Accessed October 9, 2026. https://investors.guardanthealth.com/press-releases/press-releases/2026/Guardant-Health-Announces-Approval-in-Europe-of-Guardant360-CDx-as-Companion-Diagnostic-for-AstraZenecas-ETCAMAH-camizestrant-in-Advanced-ER-positive-Breast-Cancer/default.aspx
2. Etcamah (camizestrant) in combination with a CDK4/6 inhibitor approved in the EU for 1st-line advanced ER-positive breast cancer. News release. AstraZeneca. July 23, 2026. Accessed October 9, 2026. https://www.astrazeneca.com/media-centre/press-releases/2026/etcamah-approved-eu-for-er-breast-cancer.html
3. Bidard FC, Mayer EL, Park YH, et al. First-line camizestrant for emerging ESR1-mutated advanced breast cancer. N Engl J Med. 2025;393(6):569-580. doi:10.1056/NEJMoa2502929
4. Bidard FC, Mayer EL, Park YH, et al. Updated results and an exploratory analysis of ESR1m circulating tumor DNA dynamics from SERENA-6, a phase 3 trial of camizestrant + CDK4/6 inhibitor for emergent ESR1m during first-line endocrine-based therapy and ahead of disease progression in patients with HR+/HER2– advanced breast cancer. Presented at: 2025 San Antonio Breast Cancer Symposium; December 9-12, 2025; San Antonio, TX. Abstract RF7-03.
5. Bidard F-C, Mayer E, Park YH, et al. First-line camizestrant for emergent ESR1 mutations in advanced breast cancer: final progression-free survival results 2 from the phase III SERENA-6 trial. J Clin Oncol. 2026;44(suppl 17):LBA1007. doi:10.1200/JCO.2026.44.17_suppl.LBA1007
6. April 30, 2026 meeting of the Oncologic Drugs Advisory Committee (ODAC). FDA. Accessed October 9, 2026. https://www.youtube.com/live/taCx7enN7hk
7. FDA grants accelerated approval to a new breast cancer treatment. FDA. September 4, 2026. Accessed October 9, 2026. https://www.fda.gov/news-events/press-announcements/fda-grants-accelerated-approval-new-breast-cancer-treatment?utm_medium=email&utm_source=govdelivery