Abstract
Abstract only
11527
Background: Chordoma is a rare neoplasm of the notochord that overexpresses brachyury, a transcription factor associated with epithelial-to-mesenchymal transition, metastasis, poor prognosis, and chemotherapy resistance. GI-6301 is a recombinant yeast-brachyury vaccine shown to demonstrate brachyury-specific immunogenicity, excellent safety profile, and some evidence of clinical activity in patients with chordoma in a previous phase I trial. Radiation therapy (RT) can modulate the tumor to become an immunostimulatory milieu. Preclinical studies have shown a synergistic effect combining RT with vaccine, thus prompting this clinical trial evaluating the combination of GI-6301 with RT in chordoma (NCT02383498). Methods: Adults with locally advanced, unresectable chordoma were treated on a randomized, double-blind, placebo controlled, phase 2 clinical trial. Patients received 3 doses of GI-6301 (80 x 107 yeast cells) vs placebo followed by photon or proton RT, followed by GI-6301 vs placebo until disease progression. Primary outcome was overall response rate (ORR) defined as a complete response or partial response in the irradiated tumor site at 24 months. Immune assays were conducted to evaluate immunogenicity. Due to slow accrual, an unplanned interim analysis was undertaken. Results: 24 pts were randomized and treated between May 2015 and September 2019. Vaccine was well tolerated with no dose reductions or treatment discontinuation. Treatment-related serious adverse events included: nausea/emesis (2); fatigue (2); dehydration (2); diarrhea (1); radiation necrosis (1); stroke (1); sepsis (1). There was no difference in ORR between the two arms. Pre-existing brachyury-specific T-cells were detected in the majority of patients but did not correlate with response to therapy. Most patients developed T-cell responses during therapy, regardless of treatment arm. Conclusions: There was no difference in ORR between the two arms. GI-6301 was well tolerated with toxicities related to RT, not vaccine. The trial was stopped early due to low conditional power for finding a statistical difference at the planned end of accrual, based on findings to date. Future studies will define utility of vaccines targeting brachyury in chordoma. Clinical trial information: NCT02383498 . [Table: see text]