Seth M. Pollack

Purpose: Leiomyosarcoma and liposarcoma frequently express PD-L1 but are generally resistant to PD-1/PD-L1 inhibition (immune checkpoint inhibitor). Trabectedin is FDA approved for leiomyosarcoma and liposarcoma. This study aimed to evaluate the safety and efficacy of trabectedin with anti–PD-L1 antibody avelumab in patients with advanced leiomyosarcoma and liposarcoma. Patients and Methods: A single-arm, open-label, Phase 1/2 study tested avelumab with trabectedin for advanced leiomyosarcoma and liposarcoma. The phase I portion evaluated safety and feasibility of trabectedin (1, 1.2, and 1.5 mg/m2) with avelumab at standard dosing. Primary endpoint of the phase II portion was objective response rate (ORR) by RECIST 1.1. Correlative studies included T-cell receptor sequencing (TCRseq), multiplex IHC, and tumor gene expression. Results: 33 patients were evaluable: 24 with leiomyosarcoma (6 uterine and 18 non-uterine) and 11 with liposarcoma. In Phase 1, dose-limiting toxicities (DLT) were observed in 2 of 6 patients at both trabectedin 1.2 and 1.5 mg/m2. The recommended Phase 2 dose (RP2D) was 1.0 mg/m2 trabectedin and 800-mg avelumab. Of 23 patients evaluable at RP2D, 3 (13%) had partial response (PR) and 10 (43%) had stable disease (SD) as best response. Six-month PFS was 52%; median PFS was 8.3 months. Patients with PR had higher Simpson Clonality score on TCRseq from peripheral blood mononuclear cells versus those with SD (0.182 vs. 0.067, P = 0.02) or progressive disease (0.182 vs. 0.064, P = 0.01). Conclusions: Although the trial did not meet the primary objective response rate endpoint, PFS compared favorably with prior studies of trabectedin warranting further investigation.