Abstract PO2-05-04: ELEVATE: A phase 1b/2, open-label, umbrella study evaluating elacestrant in various combinations in patients (pts) with estrogen receptor-positive (ER+), HER2-negative (HER2-) locally advanced or metastatic breast cancer (mBC)

Abstract Background: ER+/HER2- breast cancer (BC) is the most prevalent BC subtype. Endocrine therapy (ET) is the mainstay of treatment; however, development of resistance to this therapeutic approach is common in the metastatic setting. After progression on first-line treatment, both ET monotherapy and combination therapy options are available. Combinations such as everolimus + exemestane and alpelisib + fulvestrant can be associated with higher efficacy, but also significant toxicity with discontinuation rates around 25%. Also, for second-line treatment, pts who did not receive prior treatment with a CDK4/6i, the combination of fulvestrant with a CDK4/6i (palbociclib, abemaciclib, and ribociclib) are among the recommended treatment options for this pt population (NCCN, 2022). However, fulvestrant has low bioavailability and an IM injection burden. The crosstalk between the three pathways ER, PI3K/AKT/mTOR and cyclin-dependent kinases (CDK4/6) provide a rationale for the combination of elacestrant, a next-generation oral SERD, with inhibitors of these pathways that are natural targets to overcome endocrine resistance. The EMERALD trial reported significantly prolonged progression-free survival (PFS) with elacestrant vs SOC ET in pts with ER+/HER2− ESR1 mutated (ESR1-mut) mBC following disease progression on prior ET (Bidard, 2022). Elacestrant was well tolerated with a manageable safety profile. Most adverse events, including nausea, were low-grade and consistent with other endocrine therapies. The replacement of the fulvestrant backbone with elacestrant in combination with targeted agents enabling oral-oral combinations is of therapeutic interest. Methods: ELEVATE (NCT05563220) is a phase 1b/2 clinical trial that will evaluate the safety and efficacy of elacestrant combined with alpelisib, everolimus, palbociclib, abemaciclib, and ribociclib. Eligible pts must be adults with confirmed ER+/HER2− advanced or mBC, > 1 measurable lesion as per RECIST v1.1, and adequate bone marrow or organ function. The main objectives for Phase 1b are to determine the RP2D of elacestrant combined with other targeted agents. The RP2D of elacestrant and abemaciclib will be determined in the ELECTRA study (NCT05386108). The Phase 2 portion will evaluate the efficacy of elacestrant combined with other study drugs for PFS; secondary objectives include PK of the various combinations, ORR, DoR, CBR, PFS, and OS. Here we report the initial dosing from the Phase 1b portion. Results: As of June 2023, 11 pts were enrolled in the phase 1b portion of the trial, cohort 1 for all combinations: 5 pts in the elacestrant and everolimus (300 mg elacestrant QD/everolimus 5 mg QD) and 3 pts in the elacestrant and alpelisib (300 mg elacestrant QD/alpelisib 250 mg QD) and 2 patients for palbociclib and 1 patient in the ribociclib combinations. Further patient accrual is expected in phase 1b cohorts of various combinations during the second half of 2023; both safety and PK data will be provided. Conclusion: In the Phase 1b portion of ELEVATE, elacestrant is being combined with various targeted agents enabling oral-oral combinations to determine a RP2D. Recruitment is actively ongoing; safety and PK results will be presented at the meeting from the completed phase 1b cohorts. Citation Format: Hope Rugo, Aditya Bardia, Javier Cortés, Giuseppe Curigliano, Erika Hamilton, Sara Hurvitz, Sibylle Loibl, Sara Tolaney, Virginia Kaklamani, Giulia Tonini, Shannon Matheny, Kathy Puvana Theall, Joyce O'Shaughnessy. ELEVATE: A phase 1b/2, open-label, umbrella study evaluating elacestrant in various combinations in patients (pts) with estrogen receptor-positive (ER+), HER2-negative (HER2-) locally advanced or metastatic breast cancer (mBC) [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-05-04.