A multicenter, open-label, phase 2 study of odetiglucan (IMPRIME PGG) and pembrolizumab in patients with metastatic breast cancer (mBCA) who have progressed through prior hormonal therapy.

Abstract

TPS1115 Background: Hormone receptor (HR) positive/ human epidermal growth factor receptor 2-negative (Her2-) breast cancer is generally considered ‘immunologically cold’ in comparison to TNBC or Her2+ breast cancer. Keynote-028 results showed a modest ORR of 12% to anti-PD1 antibody, pembrolizumab (PEM) in previously treated HR+/ HER2-/programmed death ligand 1-positive (PD-L1-positive) advanced breast cancer patients (pts). With limited options available, there is significant unmet need to expand clinical benefit from ICI. Odetiglucan, a novel beta glucan, acts as a pathogen-associated molecular pattern (PAMP) that drives a cascade of immune activating events. It repolarizes the immunosuppressive microenvironment, activates the maturation of antigen presenting cells and significantly enhances efficacy of ICI therapy in preclinical tumor models. In a Ph2 trial (IMPRIME 1) of odetiglucan + PEM in 44 pts with heavily pretreated metastatic TNBC, an ORR=15.9%, DCR=54.5%, mDOR=12.7mo, mPFS=2.86 mo, 12 mo OS rate=57.6%, and mOS=16.4 mo were observed. Clinical benefit was particularly evident in a subset of pts, mTNBC “converters” (12/44 pts) who were originally diagnosed with ER/PR+ disease and progressed through endocrine therapies +/- CDK4/6 inhibitors. In these 12 pts, an ORR=50%, DCR=83%, mDOR=11.2, mPFS=5.6 mo, 12-mo OS rate=64.8%, and mOS=17.4 mo were observed. Methods: Odetiglucan + PEM is now being explored in pts with hormone-resistant metastatic breast cancer (MBC). This is a phase 2, Simon’s 2-Stage study of MBC pts who have progressed through prior hormonal therapy with >1 CDK4/6 inhibitor. Pts will receive odetiglucan 4 mg/kg/wk + PEM 200 mg Q3wk. Stage 1 will enroll 23 pts. If >4 pts have an objective response after 12 wks of treatment, the study will proceed to Stage 2 enrolling an additional 24 pts (N=47). Rejection of the null hypothesis requires >10 objective responses. Main eligibility criteria include: MBC having failed prior hormonal therapy with >1 CDK4/6 inhibitor, <2 chemotherapies, serum ABA ≥20 µg/mL, and no prior ICI exposure. Primary endpoint is ORR (RECIST v1.1); secondary endpoints are PFS, OS, DCR, DoR, and safety. Exploratory objectives assess impact of the treatment combination on immune activating events in peripheral blood and tumor biopsies, and correlate tumor microenvironmental changes with clinical benefit Select subpopulations may be explored. Point estimates with 95% confidence intervals (CIs) of ORR and DCR will be computed. Medians, first, and third quartiles with 95% CI will be estimated using Kaplan-Meier method for other secondary endpoints. Safety parameters will be summarized. The trial is sponsored by HiberCell, Inc. in collaboration with Merck & Co. ̃25 US sites will participate. Clinical trial information: NCT05159778.