Pharmacology and pharmacokinetics of elacestrant

Elacestrant, a novel oral selective estrogen receptor (ER) degrader (SERD), was approved by the Food and Drug Administration (FDA) on January 27, 2023, for use in patients with ER and/or progesterone receptor (PR)-positive and HER2-negative metastatic breast cancer whose tumors harbor an ESR1 missense mutation (ESR1-mut), after at least one line of endocrine therapy (ET). The FDA made its decision based on the randomized phase 3 EMERALD trial, which met its primary endpoint of improved median progression-free survival (mPFS) with elacestrant monotherapy versus standard-of-care endocrine monotherapy in the overall intention to treat population; however, this benefit was largely driven by the ESR1-mut cohort. Elacestrant is a dose-dependent mixed ER agonist/antagonist, which at high doses acts as a direct ER antagonist as well as selective downregulator of ER. It is 11% bioavailable, primarily metabolized by CYP3A4 in the liver and excreted in feces. This leads to drug-drug interactions with strong CYP3A4 inhibitors and inducers, such as itraconazole and rifampin, respectively. In accordance with its clearance route, dose reduction is recommended in patients with moderate hepatic dysfunction but not in renal dysfunction. Studies evaluating elacestrant in severe hepatic dysfunction as well as in patients from racial and ethnic minority groups are ongoing. Overall, elacestrant is the first orally bioavailable SERD approved by the FDA for use in patients with metastatic breast cancer. Current clinical trials are ongoing evaluating it in the adjuvant setting in patients with early stage ER-positive breast cancers.