The Food and Drug Administration on Thursday granted accelerated approval to a new breast cancer pill meant to be started before a patient's tumor has visibly progressed — based not on a scan, but on a mutation detected in a routine blood draw. The drug, camizestrant, will be sold under the brand name Etcamah and is approved for adults with hormone receptor-positive, HER2-negative advanced or metastatic breast cancer whose tumors develop an ESR1 mutation while they are still responding, by imaging standards, to first-line treatment with an aromatase inhibitor and a CDK4/6 inhibitor.
Regulators said it is the first cancer therapy the agency has cleared based on catching a resistance mutation in circulating tumor DNA — fragments of tumor genetic material shed into the bloodstream — before radiographic scans show the disease getting worse. "This marks the first FDA approval of a cancer therapy guided by the detection of a resistance mutation in circulating tumor DNA," said Angelo de Claro, director of the FDA's Oncology Center of Excellence. Doctors would prescribe the drug alongside a companion diagnostic blood test, Guardant360 CDx, used to identify the mutation.
What the trial found
The approval rests on SERENA-6, an AstraZeneca-sponsored, randomized, double-blind, placebo-controlled Phase III trial that enrolled 315 patients worldwide who were tested for the ESR1 mutation in their blood every two to three months while on first-line therapy. Patients found to have the mutation, with no sign yet of progression on scans, were randomly assigned either to switch to camizestrant (75 milligrams daily) alongside their existing CDK4/6 inhibitor, or to continue their aromatase inhibitor and CDK4/6 inhibitor with a matching placebo. Median progression-free survival was 16.0 months in the camizestrant group versus 9.2 months in the control group — a 56% reduction in the risk of progression or death (hazard ratio 0.44, p<0.0001).
Dr. Erica L. Mayer of the Dana-Farber Cancer Institute, an investigator involved with the trial, called the approval "welcome news," noting that "many patients with estrogen receptor-positive, HER2-negative advanced breast cancer are in urgent need of new treatments that delay disease progression in the first-line setting." The drug carries a boxed warning for cardiac arrhythmia risk when combined with certain other medications, along with warnings about slowed heart rate and potential harm to a developing fetus.
ESR1 mutations are a well-documented way hormone-driven breast tumors escape aromatase inhibitors, arising in the estrogen receptor gene as cancer cells adapt under treatment pressure; oncologists have historically only acted on them once scans confirmed the tumor had already resumed growing. Liquid biopsy testing raises the possibility of intervening earlier, though it depends on frequent blood draws and a test not yet universally reimbursed or available.
It is worth flagging what accelerated approval does and does not mean here: the FDA's decision rests on progression-free survival, a surrogate marker, rather than on mature overall-survival data, and the agency is requiring confirmatory studies to verify that the drug ultimately helps patients live longer, not just delays scan-detected progression. The trial was also funded and run by AstraZeneca, the drug's manufacturer. Oncologists are expected to begin incorporating routine ctDNA monitoring into first-line treatment plans as the drug reaches pharmacies, while the confirmatory trials needed to convert this into a full approval continue.
