Belzutifan treatment of Von Hippel-Lindau (VHL) related central nervous system (CNS) hemangioblastomas (HBs): A single institution experience

2078 Background: Patients with inactivating germline mutations in the VHL gene develop CNS (brain and/or spine) HBs and/or renal cancers, pheochromocytomas and pancreatic neuroendocrine tumors. The oral HIF2a inhibitor belzutifan has been approved by FDA for the treatment of VHL-related HBs. We present here data on a cohort of VHL patients with CNS HBs treated with belzutifan in a single institution. Methods: Adult VHL patients, with radiologically documented CNS (brain and/or spine) HBs that displayed documented growth within the last 6 months prior to therapy, were treated with an initial dose of 120 mg belzutifan orally per day. Target lesions included HBs > 0.4cm long in one maximal cross-sectional diameter. Lesions were imaged by MRI at 1.5, 3, 6 months after initiation of treatment and at 6-month intervals thereafter. Solid enhancing lesions, associated cysts and peritumoral edema were recorded and quantified. Tumor sizes were evaluated by RECIST 1.1 criteria and volumetric analysis. All patients were evaluated and treated in the Hemangioblastoma Center and the VHL Clinic of the Massachusetts General Hospital Cancer Center. Results: At the time of analysis, 9 females and ten 10 male VHL patients (n=19) have been treated. Median age at treatment initiation was 36 yo (range 19-59). Median follow up is 12 months (range 1-19.5 months). Two patients were not yet evaluable for response. Of 17 evaluable patients, 8 had a PR (ORR 47%; 95% CI, 34-60), 8 had SD and 1 patient had progression (PD, 5.8%). Two patients had dose reduction to 80 mg/d because of anemia. No patient had grade 3 or greater toxicity and no patient experienced a CNS related toxicity during treatment. Volumetric analysis of solid and cystic components of the lesions, VHL germline mutations and other correlates of response to belzutifan will be presented. Conclusions: Real world data collected at a single institution confirm the high response rate of both solid and cystic components of CNS HBs to the FDA approved HIF2a inhibitor, belzutifan. Belzutifan was well tolerated. Further prospective controlled studies addressing the optimal dose, schedule and duration of treatment of HBs with belzutifan are required.