A phase II study of a yeast-based therapeutic cancer vaccine, GI-6207, targeting CEA in patients with minimally symptomatic, metastatic medullary thyroid cancer.

Abstract

TPS3127 Background: Saccharomyces cerevisiae has been genetically modified to express CEA protein and developed under a CRADA with GlobeImmune/NCI as a heat-killed immune-stimulating, therapeutic cancer vaccine (GI-6207). A phase I study with GI-6207 demonstrated safety, biomarker stabilization and enhanced immune response in some patients. CEA is over-expressed in multiple malignancies, including medullary thyroid cancer (MTC). Two therapies recently approved by the FDA for metastatic MTC (vandetanib, cabozantinib) come with toxicity and should be reserved for symptomatic/progressive disease. However, a large population of asymptomatic MTC patients has small tumor burden and/or disease that is more indolent. The standard management of these patients is observation. Preliminary data suggest that tumor growth measured by the rate of CEA and calcitonin increase can be quantified in a 3-6 months. Retrospective data from prostate cancer studies suggest vaccines can alter growth rates within 3-4 months. We hypothesize that GI-6207 can alter tumor growth rates in MTC and impact long-term outcome. Methods: A phase II study will evaluate the effect of GI-6207 onthe rates ofincrease in calcitonin in metastatic MTC. 34 patients with minimally symptomatic, radiographically evaluable, metastatic MTC will be randomized 1:1. Arm A will receive vaccine for a year from the time of enrollment. Arm B will receive vaccine after 6 months of surveillance. GI-6207 will be administered subcutaneously at 4 sites (10 yeast units/site), every 2 weeks for 3 months, then monthly up to 1 year. The primary endpoint will compare the effect of GI-6207 on calcitonin kinetics between the vaccine and surveillance arms in the first 6 months. Secondary endpoints include immunologic responses (including antigen-specific T cell responses), objective responses, time to progression, and changes in CEA kinetics. If this trial can prospectively demonstrate that vaccines can alter tumor growth rates, and if such changes are associated with clinical outcomes, then changes in tumor growth rates may become a clinical metric to evaluate vaccine efficacy in MTC and other populations.