Patient-reported outcomes and qualitative interviews in patients with estrogen receptor-positive/human epidermal growth factor receptor 2-negative advanced breast cancer: results from the phase III EMBER-3 trial

BACKGROUND: Imlunestrant is a next-generation, brain-penetrant, oral selective estrogen receptor degrader. In the phase III EMBER-3 trial, conducted in patients with estrogen receptor-positive/human epidermal growth factor receptor 2-negative advanced breast cancer, imlunestrant demonstrated a significant progression-free survival benefit compared with standard endocrine therapy (standard of care; fulvestrant or exemestane) in patients harboring ESR1 mutations (ESR1m). Additionally, the combination of imlunestrant and abemaciclib improved outcomes compared with imlunestrant monotherapy, irrespective of ESR1m status. This manuscript reports findings from exploratory analyses of patient-reported outcome (PRO) measures and qualitative interviews evaluating EMBER-3 participants' experiences and treatment preferences. MATERIALS AND METHODS: PROs administered were the European Organisation for Research and Treatment of Cancer (EORTC) Quality of Life Questionnaire Core 30 (QLQ-C30) and the PRO-Common Terminology Criteria for Adverse Events (CTCAE) items for diarrhea frequency and injection site reactions (for fulvestrant recipients only). Mean changes from baseline in EORTC QLQ-C30 scores were calculated using a longitudinal mixed model for repeated measures; a 10-point change defined as clinically meaningful. PRO-CTCAE analyses were descriptive. Interview transcripts were analyzed using directed content analysis techniques. RESULTS: Overall, global health status/quality of life (GHS/QoL) and function were generally maintained over time across treatment arms among the ESR1m population and all patients, with treatment differences favoring imlunestrant versus SOC among the ESR1m population. Fewer GHS/QoL and function deterioration events occurred in the imlunestrant arm (ESR1m and all patients) compared with other treatment arms. Most (72.3%) fulvestrant-treated patients reported injection site reactions at any time. Diarrhea frequency was consistently higher in the combination arm of imlunestrant-abemaciclib. CONCLUSION: GHS/QoL and function were maintained across treatment arms, despite a higher incidence of diarrhea in the imlunestrant-abemaciclib group. These PRO findings complement the efficacy and safety results from EMBER-3 and further support the favorable risk-benefit profile of imlunestrant, either as oral monotherapy or in combination with abemaciclib, in patients with advanced breast cancer.