Folate Receptor Overexpression in Human and Canine Meningiomas—Immunohistochemistry and Case Report of Intraoperative Molecular Imaging

Abstract BACKGROUND Meningiomas are well-encapsulated benign brain tumors and surgical resection is often curative. Nevertheless, this is not always possible due to the difficulty of identifying residual disease intraoperatively. We hypothesized that meningiomas overexpress folate receptor alpha (FRα), allowing intraoperative molecular imaging by targeting FRα with a near-infrared (NIR) dye. OBJECTIVE To determine FRα expression in both human and canine meningioma cohorts to prepare for future clinical studies. Present a case study of a meningioma resection with intraoperative NIR fluorescence imaging. METHODS Tissue samples of 27 human meningioma specimens and 7 canine meningioma specimens were immunohistochemically stained for FRα along with normal dura, skeletal muscle, and kidney tissue. We then enrolled a patient with a pituitary adenoma and tuberculum sella meningioma in a clinical trial in which the patient received an infusion of folate-linked, NIR fluorescent dye prior to surgery. RESULTS In the cohort of human meningiomas, 9 WHO grade I, 12 grade II, and 6 grade III tumors were identified. Eighty-nine percent of WHO grade I, 67% of grade II, and 50% of grade III tumors overexpressed FRα. In the 7 canine meningioma samples, 100% stained positively for FRα. Both human and canine normal dura from autopsy samples demonstrated no evidence of FRα overexpression. In the case study, the meningioma demonstrated a high NIR signal-to-background-ratio of 4.0 and demonstrated strong FRα immunohistochemistry staining. CONCLUSION This study directly demonstrates FRα overexpression in both human and canine meningiomas. We also demonstrate superb intraoperative imaging of a meningioma using a FRα-targeting dye.