Phase II Results Utilizing the Tumor-Targeting Fluorescence Imaging Agent Tozuleristide and the Canvas Imaging System in a Cohort of Adults Undergoing Resection of Vestibular Schwannoma

Vestibular schwannomas are benign tumors of the cerebellopontine angle where extent of resection is related to facial nerve dysfunction postoperatively. Tozuleristide is a tumor-targeting near-infrared agent used in fluorescence-guided surgery to increase extent of resection. The objective of this study was to explore tozuleristide use in combination with the Canvas imaging system to determine if tozuleristide administration leads to vestibular schwannoma and facial nerve fluorescence. Adults undergoing initial resection of vestibular schwannoma received 24 mg of tozuleristide 16 to 20 hours preoperatively. The Canvas imaging system was used intraoperatively to visualize fluorescence. Intraoperative fluorescence was compared with postoperative histopathology to correlate fluorescence with tumor. Four patients were enrolled, and no patient had an adverse effect to tozuleristide administration. All tumors demonstrated strong fluorescence intraoperatively. Intraoperative fluorescence was consistent with the presence of tumor tissue on histopathology. The facial nerve was identified and stimulated in all patients. No facial nerve demonstrated fluorescence. Tumor resection was stopped when the facial nerve was no longer visualized. Two patients underwent gross total resection and two underwent subtotal resection. Three patients had House–Brackmann score of 1 postoperatively; one patient had House–Brackmann score of 2. After administration of 24 mg of tozuleristide preoperatively, all four vestibular schwannomas exhibited fluorescence. Fluorescence was specific to tumor tissue, and no facial nerve or nontumoral tissue demonstrated fluorescence. Tozuleristide may aid in the ability to differentiate tumor from cranial nerves in vestibular schwannomas. Further investigation with a larger cohort of skull base tumors is warranted.