Endocrine Abstracts

Background: As per 2014 Endocrine Society guidelines, ¹³¹I-MIBG therapy is usually reserved for metastatic or unresectable disease in patients with pheochromocytoma / paraganglioma. In this series, we describe three patients effectively treated with primary ¹³¹I-MIBG therapy. The indications were primary neo-adjuvant therapy prior to surgery, or palliative.

Case series: Case 1 – 18-year-old male with a 60 mm para-aortic paraganglioma on CT scan after a presentation with trauma. Urinary catecholamines were elevated and alpha blockade commenced. Surgical intervention was deemed of unacceptably high risk due to proximity to major mesenteric vessels. One cycle of primary ¹³¹I-MIBG therapy was administered. The lesion reduced to 53 mm on repeat imaging, now clear of vessels and amenable to resection. No complications were encountered. Case 2 – 31-year-old female with SDHB mutation, diagnosed with a 56 mm pelvic paraganglioma after presentation with a crisis. Plasma metanephrines were elevated and alpha blockade commenced. Due to a COVID-19 related surgical delay, she received a single cycle of primary ¹³¹I-MIBG therapy prior to resection, which was well tolerated. No repeat imaging was performed but the surgical specimen appeared similar in diameter to radiological measurements. Case 3 – 79-year-old female diagnosed with a 150 mm mesenteric paraganglioma after presenting with urinary discomfort. Plasma metanephrines were normal and surgery was considered too high risk due to proximity to mesenteric vessels. The lesion reduced to 120 mm after three cycles of ¹³¹I-MIBG therapy. After multidisciplinary team review, surgery was considered feasible, but conservative management was pursued due to comorbidities.

Discussion: In the cases described primary¹³¹I-MIBG therapy was well tolerated without significant side effects or precipitation of pheochromocytoma crisis. In two cases significant reduction of tumour volume was achieved. These outcomes suggest primary ¹³¹I-MIBG therapy may be a safe and effective treatment approach pre-surgery (neo-adjuvant) or for palliation without the presence of metastasis.