AstraZeneca’s camizestrant has received approval from the US Food and Drug Administration (FDA), introducing a new treatment option for some patients with advanced breast cancer.
Sold under the brand name Etcamah, camizestrant is designed for people with HR-positive, HER2-negative locally advanced or metastatic breast cancer who develop an ESR1 mutation while receiving hormone therapy and a CDK4/6 inhibitor.
What makes the approval particularly significant is the way doctors can identify patients for treatment. Instead of waiting for scans to show that the cancer has progressed, treatment can be considered after a blood test detects an emerging ESR1 mutation.
The test analyses circulating tumour DNA (ctDNA), genetic material released by cancer cells into the bloodstream. The appearance of an ESR1 mutation can indicate that the cancer is beginning to develop resistance to an existing hormone treatment.
This means doctors may be able to adjust treatment before progression becomes visible on imaging.
Results from the SERENA-6 trial showed that patients who switched to camizestrant while continuing a CDK4/6 inhibitor had a median progression-free survival of 16 months. Those who stayed on their existing treatment had a median progression-free survival of 9.2 months.
Camizestrant is an oral selective estrogen receptor degrader (SERD). It targets the estrogen receptor and reduces estrogen-driven signalling that can promote the growth of hormone-sensitive breast cancer cells.
Under the FDA approval, camizestrant can be combined with abemaciclib, palbociclib or ribociclib. The recommended dose is 75 mg once daily, with or without food.
ESR1 mutations are associated with resistance to aromatase inhibitors. They are uncommon when HR-positive metastatic breast cancer is initially diagnosed but can become considerably more common after treatment. The FDA estimates that fewer than 5% of patients have the mutation at diagnosis, compared with nearly 40% who may develop it after progression on an aromatase inhibitor.
In the SERENA-6 study, patients receiving an aromatase inhibitor and CDK4/6 inhibitor underwent blood testing alongside routine scans. Those who developed an ESR1 mutation without scan-confirmed progression were able to switch to camizestrant while continuing their CDK4/6 inhibitor.
The FDA has also approved Guardant360 CDx as a companion diagnostic for detecting ESR1 mutations in patients who may be eligible for the drug.
The agency called the decision a first for cancer treatment, saying it represents the first FDA approval of a therapy guided by a resistance mutation detected in circulating tumour DNA before imaging shows progression.
Dr. Angelo de Claro of the FDA’s Oncology Center of Excellence described the approval as a significant milestone in the use of blood-based molecular testing to guide cancer treatment.
Camizestrant was granted accelerated approval. Under this pathway, additional studies are required to confirm the drug’s clinical benefit, and continued approval may depend on confirmatory evidence.
