Phase 2 trial of mirvetuximab soravtansine plus pembrolizumab in recurrent folate receptor α-positive uterine serous carcinoma

Mirvetuximab soravtansine (MIRV) is a folate receptor alpha (FOLR1)-targeting antibody-drug conjugate with the maytansinoid payload DM4. A phase 2 trial at Dana-Farber Cancer Institute (Boston, MA) evaluated the combination of MIRV with pembrolizumab in female patients with recurrent FOLR1-expressing serous endometrial cancer (EC). Co-primary endpoints were objective response rate (ORR) and rate of progression-free survival at 6 months (PFS6). Eighteen patients initated protocol therapy (MIRV 6 mg/kg and pembrolizumab 200 mg every 3 weeks). The confirmed ORR is 28% (95% CI 10-53; one complete and four partial responses) with four patients progression-free at 6 months (PFS6 24.4%; 95% CI 7.7-46.1). Grade 3 treatment-related adverse events were rare, with no grade ≥ 4 toxicities. The trial was closed early for feasibility (planned sample size of 35 patients not reached) and hence results are considered preliminary.