Abstract
BACKGROUND: Vestibular schwannoma (VS) is a benign nerve-sheath tumor that sporadically displays aggressive behavior - often attributable to intrinsic tumor biology and an unfavorable immune microenvironment. However, the potential for idiosyncratic responses on VS growth to novel biologics is largely unknown. METHODS: Case report. RESULTS: A 57-year-old man underwent stereotactic radiosurgery (SRS) for a small intracanalicular presumed VS, which presented with left-sided hearing loss and episodic vertigo. Treatment response was excellent, with >50% reduction in tumor volume and confirmed stability at 14 years post-SRS radiographic follow-up. The patient subsequently developed an unrelated metastatic gastrointestinal tumor, and was started on tyrosine kinase inhibitors. Within 12-months of regorafenib treatment, and 16-years since SRS, the patient developed ipsilateral House-Brackmann Grade IV facial weakness. Dramatic VS expansion from 14 to 25 mm in maximum diameter, with new brain stem compression, was seen on MRI. Due to poor prognosis of his gastrointestinal malignancy, he declined surgical resection, and elected for palliative salvage SRS. CONCLUSION: We report the case of VS with radiographically proven stability for >14 years that underwent dramatic tumor progression after treatment with tyrosine kinase inhibitors. The dynamics between systemic immunomodulation and VS disease phenotype remain incompletely understood, and there may be potential for unintended iatrogenic VS progression.