S3361 A Rare Case of Malignant Peripheral Nerve Sheath Tumor Primarily Presenting in the Biliary Tract and Stomach

Introduction: Malignant peripheral nerve sheath tumor (MPNST) are rarely found in the gastrointestinal tract. In this case, we describe a rare presentation of MPNST arising in the biliary tract and gastric submucosal lesion. This case illustrates the diagnostic challenges posed in the gastrointestinal manifestation of MPNST. Case Description/Methods: A 30 year-old woman with a history of neurofibromatosis type 1 presented with cholestatic liver injury. The patient underwent endoscopic ultrasound (EUS)/endoscopic retrograde cholangiopancreatography (ERCP) revealing a smooth tapering distal common bile duct stricture at the level of the pancreatic head, without evidence of a pancreatic mass or ampullary lesion. Bile duct brushings did not reveal evidence of malignant cells. Three months later patient presented with coffee ground emesis and underwent esophagogastroduodenoscopy finding a clean based gastric ulcer in the gastric fundus with heaped up edges, concerning for a submucosal lesion. Biopsies did not have evidence of malignancy. Patient subsequently underwent multiple EUS/ERCP with fine needle aspiration (FNA) of the submucosal gastric lesion and biliary duct brushings. Eventually gastric mass FNA as well as FNA of later identified ampullary mass both revealed spindle cell morphology with SMA positivity, and “reactive changes with myofibroblasts,” though definitive pathological diagnosis was elusive. Shortly after, patient was found to have 2 neck masses, multiple bilateral breast masses, and cavitary lung lesions with biopsies revealing spindle cell morphology with high mitotic index and NGS-positivity consistent with MPNST. The patient was ultimately diagnosed with MPNST first presenting in the biliary tract, however adequate tissue sample was only able to be obtained from distal sites. She was treated with chemotherapy but unfortunately passed away from pulmonary complications. Discussion: MPNST most commonly arises in the extremities, trunk, and head and neck. It is reported to occur in about 3-15% of patients with neurofibromatosis type 1. MPNST originating from the biliary tract is extremely rare and has only been reported in 1 prior case report. In the prior case, the MPNST in the biliary tract also was seen as a smooth tapering distal biliary duct stricture, but was able to be completely resected with a good outcome. Overall, MPNST often has poor prognosis with 15-66% 5-year survival. We present a rare case of MPNST of the biliary tract arising in a patient with neurofibromatosis type 1, which initially manifested primarily as a biliary stricture with negative pathology before involving other sites.