FDA clears Etcamah to target breast cancer resistance before disease progression

Clinical takeaway: Periodic circulating tumor DNA testing can now identify emerging ESR1 mutations and trigger a switch to Etcamah before radiographic progression. The accelerated approval introduces a new biomarker-guided strategy, although confirmatory evidence of clinical benefit is still required.

FDA granted accelerated approval to Etcamah (camizestrant), an oral selective estrogen receptor degrader, in combination with abemaciclib, palbociclib, or ribociclib for adults with HR-positive, HER2-negative locally advanced or metastatic breast cancer. Eligible patients must have an ESR1 mutation detected by an FDA-authorized test while receiving first-line aromatase inhibitor plus CDK4/6 inhibitor therapy, without disease progression.

FDA also authorized Guardant360 CDx as a companion diagnostic. The decision marks the first FDA approval of a cancer therapy guided by detection of a resistance mutation in circulating tumor DNA before imaging shows progression.

In the double-blind, phase 3 SERENA-6 trial, 315 patients underwent blood testing alongside routine imaging every 2 to 3 months. When an ESR1 mutation emerged, patients were randomly assigned to switch from anastrozole or letrozole to camizestrant while continuing the same CDK4/6 inhibitor, or to remain on their existing regimen.

The camizestrant strategy reduced the risk of progression or death by 56% versus continued aromatase inhibitor therapy. Median progression-free survival was 16.0 versus 9.2 months. A subsequent analysis also favored camizestrant for time to second progression (25.7 versus 19.1 months) while overall survival remained immature. No new safety signals were identified, but labeling carries a boxed warning for irregular heart rhythm with certain concomitant medications.

“This marks the first FDA approval of a cancer therapy guided by the detection of a resistance mutation in circulating tumor DNA,” said Angelo de Claro, MD, director of FDA’s Oncology Center of Excellence.

The approval followed a closely watched review. FDA granted breakthrough therapy designation in May 2025, but its advisory committee failed to reach a majority supporting the strategy in April 2026. FDA subsequently requested additional analyses and extended the PDUFA date before granting accelerated approval on September 4; confirmatory studies must verify clinical benefit.

Source: FDA (2026 Sep 4) FDA Grants Accelerated Approval to a New Breast Cancer Treatment; AstraZeneca (2026 Sep 4) Etcamah in Combination With a CDK4/6 Inhibitor Approved in the US for 1st-Line Advanced HR-Positive Breast Cancer