The drug has been approved for adults with hormone receptor positive (HR-positive), HER2 negative, locally advanced or metastatic breast cancer whose tumours develop an ESR1 mutation during treatment with an aromatase inhibitor and a CDK4/6 inhibitor. ESR1 mutations can cause breast cancer cells to become resistant to commonly used hormone therapies. Etcamah is designed to target the estrogen receptor and help delay disease progression in patients whose tumours develop this mutation.

The FDA approval was supported by clinical trial results showing that patients receiving Etcamah with a CDK4/6 inhibitor had a median progression free survival of about 16 months, compared with 9.2 months among those continuing an aromatase inhibitor with a CDK4/6 inhibitor. The approval also marks a significant step toward using blood based genetic testing to identify treatment resistance earlier. The FDA authorised the Guardant360 CDx test alongside the drug to detect ESR1 mutations. The treatment is intended for patients whose cancer has not yet shown visible progression on scans but has developed an ESR1 mutation. This could allow doctors to identify changes in the cancer earlier and consider modifying treatment before conventional imaging confirms progression.

The development reflects the growing shift towards precision medicine in oncology, where treatment decisions are increasingly guided by the genetic characteristics of a patient's cancer. Identifying specific mutations can help doctors determine which therapies may be more suitable for individual patients. AstraZeneca will also need to conduct additional studies to confirm the long term clinical benefits of Etcamah, as the FDA has granted the drug accelerated approval. The results of these studies will be important in determining its continued regulatory status. The approval gives doctors another treatment option for a specific group of patients with advanced breast cancer and highlights the growing role of targeted therapies and molecular testing in cancer care.