SARC037: Results of phase I study of trabectedin given as a 1-hour (h) infusion in combination with low dose irinotecan in relapsed/refractory Ewing sarcoma (ES).

Abstract

11519 Background: Recurrent ES carries a poor prognosis, and systemic therapies have limited efficacy. Preclinical models suggested that trabectedin (T) could achieve serum concentrations high enough to suppress the dominant oncogene of ES (i.e. EWS::FLI1 transcription factor), and that this effect is sustained by subsequent administration of low dose irinotecan (I). We conducted a phase I study of T+I in patients (pts) with ES. Methods: This multicenter dose escalation study employed a standard 3+3 design. T was given as a 1-h infusion on day (D)1 with low dose I intravenously on D2 and 4 of a 21D cycle. Dose limiting toxicities (DLTs) were evaluated in cycle one. Eligibility required confirmed EWS::FLI1 fusion transcript, age ≥10 years, ECOG performance status ≤2, adequate organ function and willing to have a research biopsy if safely accessible. Primary objectives were to determine the recommended dose (RD) and safety of T+I. Secondary objectives comprised efficacy of T+I and avidity of ES for 3'-Deoxy-3'-18F Fluorothymidine (18F-FLT) PET. Results: 20 pts enrolled from 1/2021-12/2022 across 5 sites, 5F/15M, median age 18 years (range 10-59). Pts had received a median of 4 (range 2-9) prior therapy lines including irinotecan in 60% of pts. Grade (G) 3/4 treatment-emergent adverse events (TEAEs) occurring in ≥10% of pts were: elevated ALT/AST, elevated creatinine phosphokinase, febrile neutropenia, anemia, lymphopenia, neutropenia, and thrombocytopenia. There were 2 G5 respiratory TEAEs. 18F-FLT PET scans were obtained in 5 pts. ES tumors were 18F-FLT PET avid. Dose level (DL)2 was the RD. At DL 2 and above, there were 4 PRs, 6 SD in 14 evaluable pts (Table). Conclusions: T+I can be safely administered to heavily pretreated pts with ES, demonstrating activity at the RD with 3 PRs (n=5 evaluable). The 18F-FLT PET may be useful to understand patterns of disease progression in ES. Correlative studies will be critical to understanding the mechanism of drug activity. Given the clinical benefit seen with T+I at RD, a phase II portion in pts with ES ≥6 years old is actively accruing. Clinical trial information: NCT04067115 . [Table: see text]