The U.S. Food and Drug Administration (FDA) recently approved imlunestrant for adults living with estrogen receptor (ER)-positive, human epidermal growth factor 2 (HER2)-negative advanced or metastatic breast cancer who have mutations in the ESR1 gene.
The FDA also approved Guardant 360p CDx, a tool that can detect patients with ESR1 mutations who may be eligible to receive imlunestrant.
Imlunestrant is an estrogen receptor antagonist developed by Eli Lilly that binds to and blocks estrogen receptors on cancer cells. This prevents the cells from growing in response to estrogen in the body.
Approval was based in part on the EMBER-3 clinical trial, which included 874 patients with advanced or metastatic ER-positive, HER2-negative breast cancer. All patients previously received an aromatase inhibitor, and some had also received CDK4/6 inhibitors.
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Participants were randomized to receive either imlunestrant, an approved endocrine therapy such as fulvestrant or exemestane or a combination treatment. The investigators used Guardant 360p CDx to identify ESR1 mutations in the blood.
The trial included 256 individuals with ESR1 mutated breast cancer. Among these participants, progression-free survival was significantly greater in those receiving imlunestrant than those receiving fulvestrant or exemestane.
Furthermore, patients in the imlunestrant group had an overall response rate of 14.3% compared with 7.7% in the approved endocrine therapy group.
Adverse effects included bone and muscle pain, fatigue, diarrhea, abdominal pain and nausea. Some participants also experienced reduced levels of hemoglobin, calcium, neutrophils and platelets. Increased levels of liver enzymes, cholesterol and triglycerides were somewhat common, too.
The advised dose of imlunestrant is 400 mg orally once per day. Individuals should take the drug on an empty stomach, at least two hours before or one hour after eating.
The FDA previously granted Fast Track designation to Imlunestrant, which helped to expedite the development and review process.
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