The U.S. Food and Drug Administration (FDA) on 4 September 2026 granted accelerated approval to Etcamah (camizestrant), developed by AstraZeneca, for certain adults with hormone receptor-positive (HR+), HER2-negative, locally advanced or metastatic breast cancer in whom an ESR1 mutation is detected during treatment with an aromatase inhibitor and a CDK4/6 inhibitor. Etcamah is an estrogen receptor antagonist and is used in combination with a CDK4/6 inhibitor such as abemaciclib, palbociclib or ribociclib. The approval is notable because it allows treatment to be changed when an ESR1 resistance mutation is detected through a blood-based test, even before imaging confirms disease progression. The FDA also approved the Guardant360 CDx as a companion diagnostic to identify breast-cancer patients with ESR1 mutations who may be eligible for Etcamah. The approval was based on results from the SERENA-6 clinical trial, in which the estimated median progression-free survival was 16 months with Etcamah plus a CDK4/6 inhibitor, compared with 9.2 months for continued aromatase-inhibitor and CDK4/6-inhibitor treatment.