FDA approves blood-test-guided treatment for advanced breast cancer

The US Food and Drug Administration has granted accelerated approval to camizestrant, an oral targeted therapy that can be started when a blood test detects emerging treatment resistance, before the cancer worsens on scans.

The medicine, combined with a CDK4/6 inhibitor, is approved for adults with hormone receptor-positive, HER2-negative locally advanced or metastatic breast cancer whose tumors develop an ESR1 mutation during treatment with an aromatase inhibitor and a CDK4/6 inhibitor. The FDA also authorized a companion blood test that detects fragments of tumor DNA carrying the mutation.

In a randomized phase 3 trial involving 315 patients, those who switched from their aromatase inhibitor to camizestrant after an ESR1 mutation appeared had a median progression-free survival of 16 months. Those who remained on their original therapy had a median of 9.2 months. This represented a 56% reduction in the risk of disease progression or death.

The approval is the FDA’s first for a cancer treatment guided by a resistance mutation found in circulating tumor DNA before imaging shows progression. Important questions remain: overall survival results are not yet mature, and confirmatory studies must establish the clinical benefit. Prescribing information also includes a boxed warning about irregular heart rhythm with certain medicines, alongside warnings about slow heart rate and harm during pregnancy.