44O - Safety and efficacy results in patients who received dose modifications in the phase III MIRASOL (GOG 3045/ENGOT-ov55) trial of mirvetuximab soravtansine vs investigator’s choice chemotherapy (ICC) in platinum-resistant ovarian cancer (PROC) with high folate receptor-alpha expression

Background

Mirvetuximab soravtansine (MIRV), an antibody-drug conjugate targeting folate receptor alpha (FRα), demonstrated an improvement in progression-free survival (PFS), overall response rate (ORR), and overall survival (OS) in patients (pts) with high-grade serous PROC compared to ICC (Moore K et al. N Engl J Med 2023;389:2162-74). Here, we present safety and efficacy data in pts who received dose modifications, which are defined as dose delays, reductions, or interruptions.

Methods

453 PROC pts with high FRα expression (VENTANA FOLR1 [FOLR1-2.1] RxDx Assay) with 1-3 prior therapies were randomized 1:1 to MIRV 6 mg/kg, adjusted ideal body weight, Day 1 of a 21-day cycle or ICC: paclitaxel, pegylated liposomal doxorubicin, or topotecan. The primary efficacy endpoint was PFS by investigator, with key secondary endpoints ORR, OS, and patient-reported outcomes in hierarchical order; other endpoints included safety, tolerability, and duration of response.

Results

With a data cutoff of March 6, 2023, 124 (57%) pts in the MIRV arm and 114 (55%) pts in the ICC arm received dose modifications. The median age was 63 for MIRV and 64 for ICC. In the MIRV arm, 36% had prior bevacizumab vs. 45% in the ICC arm, and 55% had prior PARPi vs 59% in the ICC. The PFS HR was 0.58 (0.43, 0.78), OS HR was 0.45 (0.30, 0.69), favoring MIRV, and the overall response rate was 59.7% for MIRV vs. 26.3% for ICC. Compared with ICC, pts on MIRV were associated with lower rates of grade 3+ treatment-emergent AEs (53% vs 72%) and serious AEs (24% vs 39%). Treatment discontinuations occurred in 12 (10%) pts on MIRV arm vs. 25 (22%) on ICC. Ocular, gastrointestinal, and neurosensory adverse events were comparable to the intent to treat population in the respective treatment arms.

Conclusions

Dose modifications occurred at similar rates in both treatment arms. MIRV demonstrated a longer PFS, OS, and higher ORR vs ICC in patients with dose modifications. The efficacy data and the well-characterized safety profile support MIRV as the standard of care for pts with FRα positive PROC.

Legal entity responsible for the study

ImmunoGen, Inc.

Funding

ImmunoGen, Inc.

Disclosure

All authors have declared no conflicts of interest.