Abstract P2-11-01: Final pre-specified analysis of the phase II trial of the GP2+GM-CSF peptide vaccine in high risk breast cancer patients to prevent recurrence
Authors: Greene JM , Schneble EJ , Perez S , Murray JL , Berry JS , Trappey AF , Hale DF , Vreeland TJ , Clifton GT , Ardavanis A , Litton JK , Shumway NM , Papamichail M , Peoples GE , Mittendorf EA 
Published: May 2016

Introduction: We are conducting a phase II clinical trial of the GP2+GM-CSF vaccine for the prevention of breast cancer recurrence in disease-free, node-positive or high-risk node negative patients (pts). GP2 is an HLA-A2+-restricted immunogenic peptide from the HER2 protein (aa: 654-662) capable of stimulating CD8+ cytotoxic T-lymphocytes (CTLs) to recognize and destroy HER2-expressing tumor cells. Here, we present the final pre-specified analysis of our study, disease free survival (DFS) at one year from last enrolled pt.

Methods: The trial is a prospective, randomized, multi-center, placebo-controlled, single-blinded, phase I/II trial designed to evaluate the safety and clinical efficacy of GP2 in breast cancer patients. Pts with any level of HER2 (immunohistochemistry [IHC] 1-3+) expression were enrolled after standard of care therapy. Blinded HLA-A2+ pts were randomized 1:1 to receive GP2 + GM-CSF or GM-CSF alone. Pts in both treatment arms received 6 monthly intradermal inoculations during the primary vaccine series (PVS) followed by 4 booster inoculations administered every 6 months. Data was collected for demographic, safety, immunologic, and clinical recurrence. Per the statistical plan, DFS was analyzed for both intention-to-treat population (ITT; all randomized pts) and per-treatment population (PT; excluding recurrences during the PVS and second malignancies) using Kaplan-Meir methods. Continuous variables are compared using analysis of variance techniques and proportions compared with Fisher's exact test.

Results: This trial enrolled 180 pts (vaccine group n=89 and control group n=91). There were no differences in age, grade, hormone receptor status, tumor size or nodal status between groups (all p&gt;0.2). With median follow up of 36.2 months, the five-year DFS estimates did not demonstrate a difference between vaccinated (VG) and control groups (CG) with ITT (82.6% v 80.4%, p=0.96, respectively) or PT (88.9% v 84.3%, p=0.52, respectively). On further subset analysis, in HER2 3+ by IHC (or positive via FISH) pts, ITT analysis showed a DFS of 93.8% v 87.2% (VG, n=50 v CG, n=51; p=0.67, respectively) while the PT analysis revealed a DFS of 100% v 87.2% (VG, n=48 v CG, n=50; p=0.052, respectively). In ER/PR+ pts, ITT analysis showed a DFS of 88.1% v 80.6% (VG, n=54 v CG, n=60; p=0.41, respectively) while PT analysis demonstrated a DFS of 91.5% v 85.2% (VG, n=52 v CG, n=57; p=0.42, respectively).

Conclusions: The final pre-specified analysis of this randomized phase II trial of the GP2+GM-CSF adjuvant breast cancer vaccine shows no statistical differences between treatment arms. However, it does identify a particular patient population where the vaccine may have efficacy; HER2 3+ patients appear to derive the greatest clinical benefit from GP2 vaccination after trastuzumab treatment with the PT analysis nearing statistical significance. Further studies are required to confirm these findings and investigate the potential link between hormone receptor status and the induction of clinically beneficial anti-tumor immunity with this vaccine.

Citation Format: Greene JM, Schneble EJ, Perez S, Murray JL, Berry JS, Trappey AF, Hale DF, Vreeland TJ, Clifton GT, Ardavanis A, Litton JK, Shumway NM, Papamichail M, Peoples GE, Mittendorf EA. Final pre-specified analysis of the phase II trial of the GP2+GM-CSF peptide vaccine in high risk breast cancer patients to prevent recurrence. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-11-01.