Background: Saccharomyces cerevisiae has been genetically modified to express Brachyury (Br) protein and developed under a CRADA with GlobeImmune/NCI as a heat-killed immune-stimulating therapeutic cancer vaccine (GI-6301). Br is a member of the T-box family of transcription factors and is a key factor in embryonic (mesoderm) development. Chordoma, a rare tumor of the notochord (derived from mesoderm) is known to overexpress Br while expression in normal adult tissue is minimal or not present. Preclinical work has demonstrated Br specific T cells can lyse human Chordoma cells expressing Br in an MHC restricted fashion. Methods: We enrolled a cohort of 7 pts with advanced Chordoma on an expansion cohort of a phase I study (NCT01519817) and evaluated their clinical and immunologic outcomes. All pts had undergone previous radiation (median 470 days since radiation: range 111-1883). All received 40 yeast units of vaccine every 2 weeks x 7 with first restaging at day 85. If stable, pts went on to monthly dosing with restaging scans every 2 months. The primary endpoint was safety, but clinical outcomes were followed as well. Br-specific T cell responses were also analyzed by flow-cytometry intracellular staining (ICS) of CD4 and CD8 T lymphocytes for the cytokines IFN-g, TNF, and IL-2. Results: All 7 pts had undergone extensive previous treatment. Median age was 59 (41-66). Two pts had relatively stable disease for 6 and 12 months, respectively, coming on the study, and both remain stable at day 141 and 197 restaging, respectively. The remaining 5 had progressive disease at enrollment. Of those 5, 1 had a decrease in index lesions >30% at day 141 with a confirmed PR on repeat scan 4 weeks later. 1 has stable disease through day 141 restaging. The other 3 progressed at day 141 restaging. Adverse events were minimal with injection site reaction being the most common (13 events in 63 doses (21%), 6 of 7 pts (86%)). Two of 7 pts had a Br-specific T cell response by ICS. Conclusions: This cohort of pts with advanced Chordoma in the phase I study with GI-6301 vaccine demonstrated safety and enhanced immune response with a confirmed PR. These findings are encouraging and warrant further study using this vaccine in pts with Chordoma. Clinical trial information: NCT01519817.