ODP549 From Positive to Negative, a Histidine to Aspartic Acid Change in SDHB is Breaking Bad in Cardiac Paraganglioma

INTRODUCTION: Cardiac paraganglioma (PGL) are extremely rare tumors. They are derived from chromaffin cells of the neural crest. Up to 40% of PGL foster germline mutations, while some bear somatic mutations. Here, we describe a sympathetic paraganglioma presenting as a cardiac mass, found to have a novel mutation of SDHB. CLINICAL CASE: A 64-year-old man with uncontrolled type 2 diabetes mellitus presented with chest pain, progressive fatigue and unintentional weight loss. An echocardiogram demonstrated a right atrial mass. Cardiac magnetic resonance imaging showed a 6.9×5.8×4.9 cm mass in the lateral right atrial wall and right atrioventricular groove, encasing the right coronary artery. Surgical removal was attempted and aborted due to involvement of the tricuspid valve. Incisional biopsy was consistent with paraganglioma. Plasma free normetanephrine was elevated at 1.87 nmol/L (ULN 0.89 nmol/L) and plasma free metanephrine was normal at 0.14 nmol/L (ULN 0.49 nmol/L). Chromogranin A was elevated at 1,038 ng/mL (normal <93 ng/mL). Iodine-123 meta-iodobenzylguanidine scan demonstrated increased and persistent MIBG activity of the cardiac mass. Ga-68 DOTATATE PET/CT scan revealed DOTATATE avidity of the mass without evidence of distant metastatic disease. Next-generation sequencing of the specimen revealed a variant of unknown significance of SDHB H244D at a variant allele frequency of 62.2%. This missense mutation replaces the histidine to aspartic acid, resulting in changes in charge of the side chain from positive to negative. Systemic treatment with tyrosine kinase inhibitor (TKI) cabozantinib was initiated due to unresectable tumor. Three month surveillance with Ga-68 PET/CT DOTATATE scan revealed partial response to treatment. Chromogranin A and normetanephrine are trending down, suggesting biochemical response. CONCLUSION: Cardiac PGL are rare and SDHB mutations are associated with worse prognosis. This is the first case of a missense mutation of SDHB at H244D, which may be clinically relevant in characterizing cardiac paraganglioma and potential response to TKI therapy. Presentation: No date and time listed