SAT307 Intraoperative Radiofrequency Ablation Of An Unresectable Abdominal Paraganglioma Promoted Objective Tumor Response And Complete Biochemical Remission

Disclosure: I.P. de Magalhães: None. B.S. Boger: None. N.L. Gomes: None. G.L. Martins: None. L.A. Bomfim Jr: None. G.F. Fagundes: None. A.F. Afonso: None. J. Petenuci: None. F.M. Coelho: None. V. Srougi: None. F.Y. Tanno: None. J.L. Chambo: None. A. Latronico: None. M.B. Fragoso: None. A.O. Hoff: None. B.B. Mendonca: None. M.R. Menezes: None. M.Q. Almeida: None. Background: Metastatic pheochromocytoma and paraganglioma (PPGL) are incurable neuroendocrine tumors. Few reports demonstrated the efficacy of radiofrequency ablation (RFA) in achieving tumor control of metastatic lesions (usually <3 cm). However, intraoperative RFA of large and unresectable primary PPGLs was not previously demonstrated. Case Report: A 31-year-old male patient was diagnosed with symptoms of catecholamine excess, high levels of plasma metanephrines and a 9 cm retroperitoneal tumor. The patient underwent an open laparotomy, which revealed unresectable disease. Anatomopathological and immunohistochemical analysis was compatible with the diagnosis of paraganglioma. The patient was treated with 13 cycles of cytotoxic chemotherapy (cyclophosphamide, vincristine and dacarbazine) without objective tumor response by RECIST. Then, he was referred to our Institution for evaluation of additional therapies. Blood pressured was well controlled with doxazosin 16 mg/d, propranolol 40 mg/d and losartan 100 mg/d. A magnetic resonance imaging (MRI) revealed an extensive retroperitoneal mass with 9.0 x 8.6 x 6.0 cm (208 ml) that involved the inferior portion of the vein inferior vena cava, inferior mesenteric artery and infrarenal aorta. Biochemical evaluation demonstrated very high levels of plasma normetanephrine (20.2 nmol/L; normal range <0.9 nmol/L) and normal metanephrine level (0.2 nmol/L; <0.5 nmol/L). The genetic investigation showed the germline pathogenic variant c.1591delC (p.Ser198Alafs*22) in SDHB gene. I(131)-metaiodobenzylguanidine scintigraphy was negative and Ga(68)-dotatate PET-CT scan displayed a high uptake in the abdominal mass without metastatic disease. Unfortunately, lutetium(177) treatment is not available in our Institution. Due to the lack of alternative therapies, we proposed a debulking open laparotomy with intraoperative RFA in the remaining tumoral lesion. Nevertheless, the tumor did not present a clear cleavage plane with the large vessels and had a large caliber intratumoral vasculature. Intraoperative RFA was performed by a very experienced team (interventional radiologist and anesthesiologist to control blood pressure during the procedure). After 2 months, the dose of doxazosin decreased from 16 mg to 8 mg (50% reduction), plasma normetanephrines dropped to 4.6 nmol/L (79%), and the largest tumor diameter at MRI reduced to 6.8 cm (88.8 ml, 57% reduction). After 7 months of the RFA procedure, the tumor continues shrinking (4.8 cm, 45 ml, 78% reduction) and plasma normetanephrine completely normalized. Conclusion: This is the first report of intraoperative RFA of a large primary unresectable paraganglioma. The patient presented a striking clinical success, complete biochemical remission and an objective tumor response. Support: Sao Paulo Research Foundation (FAPESP) grant 2019/15873-6 (to M.Q. Almeida). Presentation: Saturday, June 17, 2023