A phase II study of Mirvetuximab Soravtansine in triple-negative breast cancer

Folate receptor alpha (FR alpha) has been reported to be expressed in up to 80% of triple-negative breast cancers (TNBC) with limited expression in normal tissues, making it a promising therapeutic target. Mirvetuximab soravtansine (mirvetuximab-s) is an antibody drug conjugate which has shown promise in the treatment of FR alpha-positive solid tumors in early phase clinical trials. Herein, are the results of the first prospective phase II trial evaluating mirvetuximab-s in metastatic TNBC. Patients with advanced, FR alpha-positive TNBC were enrolled on this study. Mirvetuximab-s was administered at a dose of 6.0 mg/kg every 3 weeks. 96 patients with advanced TNBC consented for screening. FR alpha staining was performed on tumor tissue obtained from 80 patients. The rate of FR alpha positivity by immunohistochemistry was 10.0% (8/80). Two patients were treated on study, with best overall responses of stable disease in one and progressive disease in the other. Adverse events were consistent with earlier studies. The study was terminated early due to the low rate of FR alpha positivity in the screened patient population and lack of disease response in the two patients treated. The observed rate of FR alpha positivity was considerably lower than previously reported and none of the patients had a partial or complete response. Treatment with mirvetuximab-s should only be further explored in TNBC if an alternate biomarker strategy is developed for patient selection on the basis of additional preclinical data.

Automated summary

The study evaluating mirvetuximab-s in metastatic TNBC showed a lower rate of FR alpha positivity than previously reported, with none of the treated patients showing a partial or complete response. Further exploration of treatment with mirvetuximab-s in TNBC should be based on alternate biomarker strategies and additional preclinical data.