Imlunestrant with or without abemaciclib in advanced breast cancer: safety analyses from the EMBER-3 trial

In EMBER-3 (NCT04975308), among patients with ER + , HER2- advanced breast cancer (ABC) with recurrence/progression on/after endocrine therapy (ET), imlunestrant significantly prolonged PFS versus standard ET in patients with ESR1 mutations, and imlunestrant + abemaciclib prolonged PFS versus imlunestrant in the overall population. We report the incidence, severity, timing, and management of common treatment-emergent adverse events (TEAEs), including safety profiles of select subgroups. In both imlunestrant-containing arms, the most common TEAEs were reversible, low grade, single occurrences; occurred early in treatment; and resulted in few treatment discontinuations (imlunestrant, 5%; imlunestrant + abemaciclib, 6%). TEAEs in imlunestrant+abemaciclib arm were managed with dose adjustments (61%) and supportive medication. Imlunestrant monotherapy had a similar safety profile between patients aged <65 and ≥65 years, while imlunestrant + abemaciclib had a similar safety profile to other abemaciclib+ET combinations in both age groups. Imlunestrant and imlunestrant + abemaciclib provide effective, convenient oral therapy with a favorable and manageable safety profile for patients with ER+, HER2- ABC with recurrence/progression on/after ET.