Phase Ib Study of Mirvetuximab Soravtansine, a Folate Receptor Alpha (FRα)-targeting Antibody-drug Conjugate (ADC), in Combination with Bevacizumab in Patients with Platinum-resistant Ovarian Cancer

Purpose: To evaluate the safety and clinical activity of mirvetuximab soravtansine, an antibody-drug conjugate comprising a humanized anti-folate receptor alpha (FRα) monoclonal antibody, cleavable linker, and the maytansinoid DM4, a potent tubulin-targeting agent, in combination with bevacizumab in patients with FRα-positive, platinum-resistant ovarian cancer.

Methods: Patients with platinum-resistant epithelial ovarian, fallopian tube, or primary peritoneal cancer were administered mirvetuximab soravtansine (6 mg/kg, adjusted ideal body weight) and bevacizumab (15 mg/kg) once every 3 weeks. Eligibility included FRα positivity by immunochemistry and prior bevacizumab exposure was permitted. Adverse events, tumor response, and progression-free survival (PFS) were determined.

Results: Sixty-six patients, with a median of 3 prior lines of therapy (range, 1-8), received the combination of mirvetuximab soravtansine and bevacizumab at full dosing during the escalation and expansion stages of the study. Adverse events were generally mild-to-moderate (≤grade 2) with diarrhea, blurred vision, nausea, and fatigue being the most common treatment-related toxicities. Six cases of pneumonitis (9%; all grade 1 or 2), an adverse event of special interest, were observed. The confirmed objective response rate (ORR) was 39%, including 5 complete responses and 21 partial responses, and the median PFS was 6.9 months. The combination was particularly active in the subset of patients (n = 16) who were bevacizumab-naïve, less heavily pretreated (1-2 prior lines), and whose tumors exhibited medium/high FRα expression (ORR, 56% with a median duration of response of 12 months; PFS, 9.9 months).

Conclusion: The combination of mirvetuximab soravtansine with bevacizumab is well tolerated in patients with platinum-resistant, recurrent ovarian cancer. The encouraging efficacy measures compare favorably to reported outcomes for bevacizumab combined with standard chemotherapy in similar patient populations.