Characterization of folate receptor alpha (FRα) expression in archival tumor and biopsy samples from relapsed epithelial ovarian cancer patients: A phase I expansion study of the FRα-targeting antibody-drug conjugate mirvetuximab soravtansine

Abstract

Purpose: To characterize folate receptor alpha (FRα) expression in archival and fresh biopsy tumor samples from relapsed ovarian cancer patients.

Methods: Patients with ovarian tumors amenable to biopsy were eligible to enroll. Eligibility included a minimum requirement of FRα positivity in archival tumor samples (≥25% of cells with ≥2+ staining intensity). Patients received mirvetuximab soravtansine at 6mg/kg once every 3weeks. Core needle biopsies were collected before and after treatment and FRα levels assessed by immunohistochemistry. Descriptive statistics were used to summarize the association between receptor expression and response.

Results: Twenty-seven heavily pre-treated patients were enrolled. Six individuals (22%) did not have evaluable pre-treatment biopsies due to insufficient tumor cells. The concordance of FRα expression in archival and biopsy tissues was 71%, and no major shifts in receptor expression were seen in matched pre- and post-treatment biopsy samples. Adverse events were generally mild (≤grade 2) with keratopathy (48%), fatigue (44%), diarrhea, and blurred vision (each 37%) being the most common treatment-related toxicities. The confirmed objective response rate (ORR) was 22%, including two complete responses and four partial responses. Superior efficacy measures were observed in the subset of patients with the highest FRα levels (ORR, 31%; progression-free survival, 5.4months).

Conclusion: Concordance of FRα expression in biopsy versus archival tumor samples suggests that archival tissue can reliably identify patients with receptor-positive tumors and is appropriate for patient selection in mirvetuximab soravtansine clinical trials. Regardless of the tissue source analyzed, higher FRα expression was associated with greater antitumor activity.

Keywords: Antibody-drug conjugate; Biopsy; Clinical trial; Folate receptor alpha; Ovarian cancer.

Fig. 1.

FRα expression scoring and receptor levels while on treatment with mirvetuximab soravtansine. (A) Representative low, medium, and high staining patterns for FRα (25–49%, 50–74%, and ≥75% of cells with ≥2+ intensity, respectively) from archival tumor specimens. (B) Comparative FRα expression in matched pre- and post-treatment biopsy samples (N = 17). Color coding is based on receptor expression scored for pre-treatment specimens; individual samples are plotted according to Cycle 2, Day 8 groupings. Very low/Negative, <25% of cells with ≥2+ staining intensity.

Fig. 2.

Percent tumor change in target lesions by archival and pre-treatment biopsy FRα expression. Data are presented from 22 and 13 patients (archival and biopsy, respectively) as target lesion measurements and/or tumor samples evaluable for IHC were not available for some individuals.