OR29-3 High-specific-activity Iodine 131 Metaiodobenzylguanidine for the Treatment of Advanced Pheochromocytoma and Paraganglioma: A Real-world Study

INTRODUCTION: Metastatic pheochromocytomas/paragangliomas (mPPGLs) are rare tumors with limited treatment options. High-specific-activity 131I-meta-iodobenzylguanidine (HSA 131I-MIBG) is the only approved therapy for mPPGLs. We summarized the efficacy and safety profile of HSA 131I-MIBG in patients with mPPGL. METHODS: This is a retrospective cohort study in patients with mPPGL treated with HSA 131I-MIBG on label at a tertiary cancer center. The primary endpoint was radiographic treatment response determined with CT/MRI according to RECIST v1.1 and 123 I-MIBG scan. Secondary endpoints were blood pressure changes and HSA 131I-MIBG related adverse events. We correlated responses with the genetic background as an exploratory endpoint. RESULTS: Twenty-four patients were treated including 15 men (62%). Median age at the time of treatment was 44 years (range 18–82). Twenty-three patients had distant metastases and one patient had an unresectable primary tumor. Seventeen patients (70%) had hormonally active tumors and 17 patients (70%) were on antihypertensive medications before HSA 131I-MIBG therapy [7 patients on alpha-blockers only and 10 on combination antihypertensive therapy]. Thirteen patients (54%) previously received antineoplastic treatment. Eleven patients (46%) received one dose of HSA 131−I-MIBG, the remaining received two doses. Median duration of follow-up was 15 months (range 2–52). In 23 evaluable patients, radiographic responses included: 2 complete responses (CR), 10 partial responses (PR), 8 stable diseases (SD), 2 mixed responses (MR), and 1 progressive disease (PD) yielding disease control rate (DCR) of 87%. Median time to response was 12.5 months (95% CI, 4.6 to 25.1). Radiographic responses in patients with sporadic disease were [6/11 SD, 3/11 PR, 1/11 MR, 1/11 PR], while the response in patients with a genetic mutation (SDHB, VHL, RET) was [2/12 CR, 7/12 PR, 2/12 SD, 1/12 MR]. In 17 hormonally active tumors, plasma metanephrines normalized in 3(18%), improved by 50% in 5(29%), increased in 4(24%), 4 patients (24%) had no repeat levels and one had stable levels. Blood pressure was evaluable in 22 (92%) patients. Blood pressure normalized in 9 patients (41%) leading to discontinuation of antihypertensive therapy. One patient had an improvement in the blood pressure leading to a reduction of antihypertensive medications. The most common adverse events were grade I/II nausea/vomiting and transient bone marrow suppression. One patient developed premature ovarian failure. Grade III/IV myelosuppression was seen in 3/24 (12%) patients. One patient had fatal pneumonitis, and one patient developed fatal gastrointestinal bleeding a month after treatment with unclear attribution to HSA 131 −I-MIBG. CONCLUSIONS: In mPPGL, HSA 131I-MIBG is associated with high DCR regardless of underlying genetic mutation. Severe adverse events are infrequent but can be fatal. Presentation: Tuesday, June 14, 2022 10:15 a.m. - 10:30 a.m.