MON-916 Pure Large Cell Neuroendocrine Carcinoma (LCNEC) of the Gall Bladder in a Patient with Down Syndrome - a Rare Case of an Aggressive Tumor of the Gall Bladder

Background: Pure large cell neuroendocrine carcinoma of the gall bladder (LCNEC-GB) is an extremely rare entity, with only 12 such cases reported in literature to date. None has been reported in a patient with genetic disorders. We describe the case of a patient with pure LCNEC-GB in the presence of Down syndrome and prior biliary atresia. Case: A 49-year-old female with Down Syndrome and history of neonatal surgery for congenital duodenal atresia presented with fever, vague abdominal discomfort and 6 month history of 15 pound weight loss. CT abdomen revealed a 5 X 4.2 cm exophytic, heterogeneously enhancing mass in the gall bladder fossa extending into segment 4B-5 of liver with mild intrahepatic biliary dilation, along with a 9 cm cystic lesion in continuity with the duodenum which was confirmed to a dilated duodenal anastomosis (from prior biliary surgery) on endoscopy. There was high suspicion for malignancy (gall bladder carcinoma versus intrahepatic cholangiocarcinoma) and subsequent metastatic workup including tumor markers, staging CT chest, MRI of the abdomen and diagnostic laparoscopy was negative. The patient underwent robotic converted to open en bloc resection of the gallbladder mass with segment 4B-5 liver resection and adherent loops of small bowel as well as resection of the dilated duodenal anastomosis followed by reconstruction with a gastrojejunostomy and Roux-en-Y/small bowel entero-enterostomy and closure of duodenotomy. Pathology demonstrated poorly differentiated “pure” large cell neuroendocrine carcinoma (G3), 6 cm in greatest dimension, with invasion of liver, duodenum and stomach, negative liver and gastric/small bowel margins. Lymphovascular invasion (LVI) was present with no perineural invasion (PNI), and 3/15 lymph nodes involved. Staging was determined to be pT4pN1. Patient was considered for adjuvant chemotherapy based on few case reports (platinum/etoposide) but unfortunately developed systemic complaints of fevers, fatigue, pain in bones and joints 2 months post operatively. Workup revealed metastatic disease which was confirmed on biopsy. Several small satellite liver lesions were also identified which was consistent with metastatic hepatic disease. Patient and family elected to proceed with hospice. Patient died within 4 months of surgery. Conclusion: Pure LCNEC-GB is an extremely rare and aggressive tumor with a poor prognosis as seen in our patient. This is the first reported case of pure LCNEC-GB in a patient with a genetic syndrome, although it is unknown if it had any causal relationship with the tumor. Prior biliary atresia/post -surgical inflammation may have also contributed to its pathogenesis by plausible development of metaplasia and expression of neuroendocrine cells which are normally absent in the gall bladder. Our case might help shed some light into pathogenesis and genetic basis if any of this rare entity.