OR25-07 A Multi-Center, Open-Label, Pivotal Phase 2 Study of Azedra® (HSA I-131-MIBG) in Patients with Unresectable, Locally Advanced or Metastatic Pheochromocytoma or Paraganglioma: Updated Long-Term Survival and Safety

Background: Pheochromocytoma/Paraganglioma (PPGL) are rare neuroendocrine tumors with a 5-yr survival rate as low as 12%. There is a high unmet medical need for effective treatment options for patients with advanced disease. AZEDRA®, a high-specific-activity iodine-131 meta-iodobenzylguanidine (HSA I-131-MIBG), is the first and only FDA-approved therapeutic radiopharmaceutical agent indicated for the treatment of adult and pediatric patients with iobenguane scan positive, unresectable, locally advanced or metastatic PPGL who require systemic anticancer therapy. Methods: Patients with advanced PPGL who were heavily pre-treated and were ineligible for curative surgery or chemotherapy received a dosimetric dose followed by up to two therapeutic doses (each at 296 MBq/kg to a max of 18.5 GBq). The primary endpoint, defined as the proportion of patients with at least 50% reduction of all antihypertensive medication(s) lasting ≥6 months, was met and previously reported. Updated secondary endpoints including overall survival (OS) and safety are reported. Results: A dosimetric dose of HSA I-131-MIBG was administered to 74 patients. Of those, 68 patients received one therapeutic dose and 50 received two doses of HSA I-131-MIBG. Clinical benefit rates (objective tumor responses defined by RECIST 1.0 and stable disease) were observed in 71.4% and 98.0% of patients receiving one and two therapeutic doses, respectively. As of October 10, 2019, median survival time for all patients was 43.2 months (95% CI 31.4, >60). Median survival time was 19.3 months (95% CI 4.5, 32.4) and 49.1 months (95% CI 36.9, >60) in patients receiving one and two doses, respectively. The overall survival was 73.8% at 2 yrs, 47.5% at 4 yrs and 41.5% at 5 yrs. The most common (≥50%) adverse events were nausea, fatigue, and myelosuppression. Myelosuppressive events resolved within 4-8 wks without requiring stem cell transplantation. Late radiation toxicity included 7 patients with secondary malignancies (myelodysplastic syndrome (MDS), acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), colon cancer, and lung carcinoma) of which MDS, ALL and AML were considered related to I-131 radiotherapy. Conclusions: Results from this pivotal phase 2 study suggest that HSA I-131-MIBG is an efficacious and safe treatment for advanced PPGL.