Abstract OT2-11-01: EMBER-3: A randomized phase 3 study of LY3484356, a novel, oral selective estrogen receptor degrader vs investigator’s choice of endocrine therapy of either fulvestrant or exemestane, in patients with estrogen receptor-positive, human epidermal growth factor receptor 2-negative, locally advanced or metastatic breast cancer previously treated with endocrine-based therapy

Abstract Background: The estrogen receptor (ER) is the key therapeutic target for ER-positive (ER+), human epidermal growth factor receptor 2-negative (HER2-) breast cancer. Novel degraders of ER may overcome resistance to available endocrine therapy (ET) while providing consistent oral bioavailability and convenience of administration. LY3484356 is a novel, orally bioavailable selective estrogen receptor degrader (SERD) with pure antagonistic properties resulting in sustained inhibition of ER-dependent gene transcription and -cell growth. In the phase 1a/b EMBER trial, LY3484356 monotherapy demonstrated a favorable safety profile with pharmacokinetic (PK) exposures that exceeded fulvestrant. LY3484356 also showed single agent efficacy in patients with ER+, HER2- metastatic breast cancer (MBC), including in patients with baseline ESR1 mutations and fulvestrant- and/or CDK4/6 inhibitor- refractory disease1. Trial Design: EMBER-3 is a randomized, open-label, global phase 3 study comparing LY3484356 versus investigator’s choice of ET (fulvestrant or exemestane), in patients with ER+, HER2- locally advanced or MBC. Approximately 500 patients will be randomized 1:1 to receive LY3484356 (400 mg PO QD continuously in 28-day cycles) or investigator’s choice of ET (dosed per label). Males and pre-menopausal women will receive concomitant treatment with a GnRH agonist. Eligibility criteria: Eligible patients are adult males and females (pre- or post-menopausal) with ER+, HER2- locally advanced or MBC who have received prior treatment with an aromatase inhibitor, alone or in combination with a CDK4/6 inhibitor. No other prior therapy for advanced disease is permitted. Patients must have evaluable disease (measurable or non-measurable bone only). Study endpoints: The primary endpoint is investigator-assessed progression-free survival (PFS) per RECIST v1.1. Secondary endpoints include BIRC-assessed PFS, overall survival, objective response rate, duration of response, clinical benefit rate, safety and tolerability, PK and patient reported outcomes. Recruitment for the EMBER-3 study begins in Q3 2021. Reference: 1Jhaveri et al. J Clin Oncol 2021 39:15_suppl, 1050 Citation Format: Komal Jhaveri, Nadia Harbeck, Philippe Aftimos, Sung-Bae Kim, Xavier Pivot, Cristina Saura, Giuseppe Curigliano, Monica Casalnuovo, Xuejing Aimee Wang, Suzanne R.L. Young, Lillian Smyth, Joyce O'Shaughnessy. EMBER-3: A randomized phase 3 study of LY3484356, a novel, oral selective estrogen receptor degrader vs investigator’s choice of endocrine therapy of either fulvestrant or exemestane, in patients with estrogen receptor-positive, human epidermal growth factor receptor 2-negative, locally advanced or metastatic breast cancer previously treated with endocrine-based therapy [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT2-11-01.