Abstract CT232: A randomized, multicenter, placebo-controlled, phase III study to evaluate the efficacy and safety of HER2/neu peptide GLSI-100 (GP2 + GM-CSF) in patients with residual disease or high-risk PCR after both neo-adjuvant and postoperative adjuvant anti-HER2 therapy, Flamingo-01

Abstract

Abstract Background: GP2 is a biologic nine amino acid peptide of the HER2/neu protein delivered in combination with Granulocyte-Macrophage Colony Stimulating Factor (GM-CSF) that stimulates an immune response targeting HER2/neu expressing cancers. In a prospective, randomized, single-blinded, placebo-controlled, multicenter Phase IIb study, no recurrences were observed in the HER2+ population after 5 years of follow-up, if the patient received the 6 primary intradermal GLSI-100 injections (p = 0.0338). Immunotherapy elicited a potent response measured by skin tests and immunological assays. Of the 146 patients that have been treated with GLSI-100 over 4 clinical trials, GLSI-100 was well-tolerated and no serious adverse events were observed considered related to the immunotherapy. Trial Design: This Phase 3 trial is a prospective, randomized, double-blinded, multi-center study. After 1 year of trastuzumab-based therapy, 6 intradermal injections of GLSI-100 or placebo will be administered over the first 6 months and 5 subsequent boosters will be administered over the next 2.5 years for a total of 11 injections over 3 years. The participant duration of the trial will be 3 years treatment plus 1 additional year follow-up for a total of 4 years following the first year of treatment with trastuzumab-based therapy. Patients will be stratified based on residual disease status at surgery, hormone receptor status, prior pertuzumab therapy and region. Approximately 498 patients will be enrolled. To detect a hazard ratio of 0.3 in invasive breast cancer free survival (IBCFS), 28 events will be required. An interim analysis for superiority and futility will be conducted when at least 14 events have occurred. This sample size provides 80% power if the annual rate of events in placebo patients is 2.4% or greater. Up to 100 non-HLA-A*02 subjects will be enrolled in an open-label arm. Eligibility Criteria: The patient population is defined by these key eligibility criteria: 1. HER2/neu positive and HLA-A*02 2. Residual disease or High risk pCR (Stage III at presentation) post neo-adjuvant therapy 3. Exclude Stage IV 4. Completed at least 90% of planned trastuzumab-based therapy Trial Objectives: 1. To determine if GP2 therapy increases IBCFS 2. To assess the safety profile of GP2 3. To monitor immunologic responses to treatment and assess relationship to efficacy and safety Accrual: Site selection and study start-up is in progress at multiple sites. Target enrollment is 598 subjects. Contact information: Snehal Patel Greenwich LifeSciences, Inc. Stafford, TX Email: snehal.patel@greenwichlifesciences.com Website: greenwichlifesciences.com Funding: This trial is supported by Greenwich LifeSciences. Citation Format: Snehal S. Patel, Jaye Thompson, Mira S. Patel, F. Joseph Daugherty, C. Kent Osborne, Mothaffar F. Rimawi. A randomized, multicenter, placebo-controlled, phase III study to evaluate the efficacy and safety of HER2/neu peptide GLSI-100 (GP2 + GM-CSF) in patients with residual disease or high-risk PCR after both neo-adjuvant and postoperative adjuvant anti-HER2 therapy, Flamingo-01 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT232.