S3393 Incidental IPMN in McCune-Albright Syndrome: A Case for Expanding Genetic Risk Stratification for Pancreatic Neoplasia

Introduction: McCune-Albright Syndrome (MAS) is a rare mosaic genetic disorder caused by postzygotic activating mutations in the GNAS gene. It is classically characterized by fibrous dysplasia, café-au-lait macules, and endocrinopathies. Pancreatic intraductal papillary mucinous neoplasms (IPMNs) are cystic pancreatic tumors, with main duct IPMNs having a high risk of malignant transformation. Herein, we present a rare case of MAS with incidental detection of IPMN, raising important questions about cancer risk and surveillance in this population. Case Description/Methods: A 51-year-old woman with a history of McCune-Albright syndrome (MAS) and IBS-C presented to our clinic for abnormal imaging. The patient had an magnetic resonance imaging of the abdomen with contrast for evaluation of a benign neoplasm of the right adrenal gland. Magnetic resonance imaging revealed an incidental cystic tubular structure anterior to the common bile duct, measuring approximately 4.5 cm × 1 cm, with small outpouchings adjacent to it. Labs: alkaline phosphatase, 338 IntlUnit/L (normal range; 44-121). Esophagogastroduodenoscopy revealed multiple gastric polyps which were resected and pathology was benign. Endoscopic ultrasound revealed dilated pancreatic duct in the pancreatic head with a sudden transition to normal size at the level of the genu, suggestive of main duct IPMN. The pancreatic duct measured up to 7-8 mm in diameter. During endoscopic retrograde cholangiopancreatography (ERCP), the major papilla appeared patulous with mucin, giving a fish-mouth appearance. There was marked dilatation of the ventral pancreatic duct in the head of the pancreas to about 10-11 mm from the level of the ampulla with sudden transition to normal size duct at the genu, consistent with IPMN. FNA specimen was negative for malignant cells and mostly mucinous material and scattered inflammatory cells. The patient was counseled on the risk of pancreatobiliary malignancy and referred to the surgical service for evaluation. Discussion: IPMNs are mucin-producing neoplasms of the pancreas that carry malignant potential. Activating GNAS mutations are frequently identified in IPMN and play a key role in tumorigenesis. MAS, caused by somatic GNAS mutations, shares this molecular alteration, yet its association with pancreatic neoplasia remains poorly defined. The incidental finding of IPMN in a patient with MAS raises the possibility that this mosaic disorder may confer an increased risk for pancreatic cystic neoplasms. Given the shared genetic pathway, it is plausible that patients with MAS represent an underrecognized high-risk group for pancreatic cancer.