I-131 MIBG therapy has been used as the first line therapy in pheochromocytoma

1452 Introduction: 131I-MIBG therapy has been used as the first line therapy in pheochromocytoma Background: Pheochromocytoma is a tumor arising from the adrenal medulla. Extra adrenal pheochromocytoma is known as paraganglioma. Surgical resection of the primary is the treatment of choice. External beam radiation and chemotherapy is less effective due to well differentiated nature. I-131Metaiodobenzylguanidine (131I-MIBG) has been used to treat malignant pheochromocytoma. I-131 MIBG was approved by FDA as a diagnostic agent in 1994. Since then our institute like few others in US was using I-131 MIBG as an investigational drug and for compassionate therapy. We present two cases treated after 1997 where we used I-131 MIBG as a neoadjuvant agent (Azedra) in preperation of the patient for surgery. The FDA approved I-131 MIBG as a therapeutic agent in 2018. Recent NCCN guidelines also mention I-131 MIBG as a first line treatment in patients with a locally unresectable lesion. Materials and Methods: 37 year old male patient presented with multiple hospital attendances of chest pain, hypertension was incidentally found to have a right adrenal mass on ultrasound. A MIBG scan showed involvement of the vertebral body at lumbar 1-2, as well as cervical 7 and subseuqntly had a biopsy proven pheochromocytoma. Subsequent to the scan, the mass was considered inoperable and it was decided to give the patient a trial of MIBG therapy to reduce the size of the mass. Patient was administered three cycles of MIBG therapy with 295mCi, 250mCi, and 300mCi of MIBG in the years 1998, 1999, and 2001 before his surgery in 2002. The second patient is a 34 year old female with medical history of Lynch syndrome. While getting a prophylactic hysterectomy was found to have liver lesions, which when biopsied returned as metastatic neuroendocrine tumor. A I-123 MIBG scan showed primary in organ of Zuckerkandl measuring about 1.6 x 2.9cm on SPECT/CT images. She had a significant tumor burden in liver, bones and primary tumor. Results: Both these patients had an improvement in functionality in life after I-131 MIBG treatment. First one got operated and had two subsequent I-131 MIBG therapies. He did well for 8 years therafter. The second patient is still following up with us and is being planned for surgery. She feels much better after two therapies with no abnormality in liver function tests or hypertensive crises. Discussion: A Dutch group has studied the use of I131 MIBG therapy in patients with stage IV neuroblastoma as the first line treatment and have found an OS benefit if MIBG was used as a neoadjuvant therapy. Our patient had the use of I131 MIBG to reduce the size of the mass to an operable size for surgery and the use was a neoadjuvant use. Conclusions: I-131 MIBG therapy can be used as a neoadjuvant therapy to reduce tumor mass and size, and thus is also a first line treatment. Both our patients had an improvement in their functional aspect of life and also had no hypertensive crises or tumor lysis syndrome even though both had a large tumor burden. Thus we conclude that I-131 MIBG is a safe therapy and should be considered preoperatively to reduce tumor size if it is needed. MIBG therapy can be used as a neoadjuvant therapy to reduce tumor mass and size, and thus is also a first line treatment.