FDA Approves Breast Cancer Drug That Targets Resistance Before Scans Show Progression

By Mintesinot Nigussie  |  September 5, 2026

The US Food and Drug Administration has approved a new treatment for advanced breast cancer that targets drug resistance detected through tumour DNA in the blood, opening a path to changing therapy before scans show the disease has progressed.

The FDA granted accelerated approval to Etcamah (camizestrant), in combination with a CDK4/6 inhibitor, for adults with hormone receptor-positive, HER2-negative locally advanced or metastatic breast cancer who develop an ESR1 mutation while receiving an aromatase inhibitor and CDK4/6 inhibitor.

ESR1 mutations are a common mechanism by which hormone receptor-positive breast cancers become resistant to aromatase inhibitors. While fewer than five per cent of patients have the mutations when metastatic disease is first diagnosed, the proportion rises to nearly 40 per cent after progression on aromatase inhibitor treatment.

The approval marks the first FDA authorisation of a cancer therapy guided by detection of a resistance mutation in circulating tumour DNA before imaging shows disease progression, according to the agency.

In the clinical trial supporting the approval, patients who switched to Etcamah plus a CDK4/6 inhibitor had a median progression-free survival of 16 months, compared with 9.2 months among those who continued their existing aromatase inhibitor and CDK4/6 inhibitor treatment.

The approach relies on blood-based testing to identify molecular signs that the cancer is becoming resistant to treatment. Guardant360 CDx has been authorised as the companion diagnostic for detecting ESR1 mutations.

Because the approval was granted under the FDA's accelerated pathway, however, evidence that acting at the point of mutation detection improves clinical outcomes compared with waiting for confirmed disease progression remains to be established. Confirmatory studies will be required.

The approval also carries warnings, including risks of irregular heart rhythms and slow heart rate, as well as fetal harm.

Source: FSX Business News