Abstract OT1-18-07: 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
Authors: Patel Snehal S , McWilliams David B , Fischette Christine T , Thompson Jaye , Daugherty F. Joseph , Osborne C. Kent , Rimawi Mothaffar F 
Published: March 2022

Background: GP2 is a biologic nine amino acid peptide of the HER2/neu protein delivered in combination with an FDA-approved immunoadjuvant Granulocyte-Macrophage Colony Stimulating Factor (GM-CSF, Sargramostim, Leukine) that stimulates an immune response targeting HER2/neu expressing cancers. In a prospective, randomized, single-blinded, placebo-controlled, multicenter Phase IIb clinical trial, no recurrences were observed in the HER2/neu positive adjuvant setting after median 5 years of follow-up, if the HLA-A*02 patient received the 6 primary intradermal GLSI-100 injections over the first 6 months (p = 0.0338) in a pre-specified subgroup analysis. Furthermore, the immunotherapy elicited a potent immune response measured by local skin tests and immunological assays. Of the 138 patients that have been treated with GLSI-100 to date over 4 clinical trials, GLSI-100 was well-tolerated and no serious adverse events were observed related to the immunotherapy. This Phase III trial aims to reproduce the Phase IIb trial and will explore the use of GLSI-100 as adjuvant therapy to increase invasive disease-free survival in HER2/neu positive and HLA-A*02 patients, post-surgery and following the first year of treatment with any trastuzumab-based therapy. Method: This Phase 3 trial is a prospective, randomized, double-blinded, multi-center study. After 1 year of trastuzumab-based therapy or an approved biosimilar, 6 intradermal injections of GLSI-100 or placebo (Bacteriostatic Saline/WFI) will be administered for the primary immunization series 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 of treatment. 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. An interim analysis is planned, and patients will be stratified based on prior and current treatments. Study Size - Interim Analysis: Approximately 498 patients will be enrolled. To detect a hazard ratio of 0.3 in IDFS, 28 events will be required. An interim analysis for superiority and futility will be conducted when at least half of those events, 14, have occurred. This sample size provides 80% power if the annual rate of events in placebo-treated patients is 2.4% or greater. Eligibility Criteria: The patient population is defined by these key eligibility criteria:

Trial Objectives:

Contact information: Website: greenwichlifesciences.com. Funding: This trial is supported by Greenwich LifeSciences.

Citation Format: Snehal S Patel, David B McWilliams, Christine T Fischette, Jaye Thompson, 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 [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 OT1-18-07.