CTNI-15. PILOT STUDY OF HIGH-DOSE PEMETREXED FOR PROGRESSIVE CHORDOMA

Abstract INTRODUCTION Chordomas are ultra-rare tumors of the spine, and no systemic therapy is approved for refractory disease. Pemetrexed is a multitargeted antifolate that inhibits thymidylate synthase (TS) and other enzymes involved in nucleotide biosynthesis. Considering the majority of chordomas do not express TS, we sought to evaluate the therapeutic activity and safety of high-dose pemetrexed. METHODS Adults with previously-treated chordoma were enrolled on an open-label, single-institution, single-arm, pilot clinical trial. Pemetrexed 900 mg/m2 was administered intravenously every 3 weeks, with supportive medications of folic acid, vitamin B12, and dexamethasone. The primary endpoint was objective response rate according to RECIST v1.1. Secondary and exploratory endpoints included adverse events, progression-free survival (PFS), tumor molecular profiles, and alterations in potential tissue and blood-based biomarkers before and after treatment. RESULTS Fifteen patients with chordoma received a median of 15 (range 4-31) doses of pemetrexed. Median PFS was 10.5 months (95% CI 9 months-undetermined) and 6-month PFS was 67%. Out of 14 response-evaluable patients, two (14%) achieved a partial response and ten (71%) demonstrated stable disease. Adverse events were generally mild at grades 1-2, the most common being fatigue, rash, nausea, constipation, diarrhea, mucositis, vomiting, alopecia, pruritus, lower extremity edema, and alanine transaminase increased. One Grade 3 creatinine increase, one Grade 3 lymphopenia, and one Grade 4 lymphopenia occurred and there were no Grade 5 adverse events, unexpected toxicities, or dose-limiting toxicities. Clinical improvement in disease-related symptoms occurred in several patients. Tumor molecular profiling revealed low mutational burden and though not statistically significant, positive TS expression trended negatively with disease progression. Cell-free microRNAs (cfmiRs) were concordantly detected in plasma and tissues and a blood cfmiR signature was identified that distinguished chordoma from health donors. CONCLUSION High-dose pemetrexed is safe and well-tolerated in chordoma patients. A phase II study is in development. (NCT03955042)