Background Imlunestrant is a next-generation, brain-penetrant, oral SERD. The EMBER-3 trial reported significant progression-free survival (PFS) improvement with imlunestrant over standard therapy (SOC; fulvestrant or exemestane) in patients with ESR1 mutations, and with imlunestrant plus abemaciclib over imlunestrant in all patients, regardless of ESR1 mutation.