A Case of Small-Cell Neuroendocrine Carcinoma of the Gallbladder in a Background of High-Grade Biliary Intraepithelial Neoplasia

Introduction/Objective Neuroendocrine carcinoma (NEC) of the gallbladder is a very rare neoplasia comprising 4% of all malignant gallbladder neoplasms. Most of NECs show molecular accumulation of TP53, while KRAS mutations are rare. Approximately 40% of Biliary intraepithelial neoplasia (BilIN) cases are associated by KRAS mutations as an early molecular event, whereas TP53 mutation appears to be a late molecular event. Methods We report a case of a 62-year-old male who presented to emergency department for evaluation of abdominal pain associated with vomiting. Imaging studies demonstrated a distended gallbladder with small amount of pericholecystic fluid along with 5 mm calculus at the gallbladder neck consistent with symptomatic cholelithiasis and acute cholecystitis. No mass lesion was radiologically identified. A laparoscopic cholecystectomy was performed. Grossly, there was a thickened area of mucosa at the distal body-fundus, measuring 5.0 x 4.5 cm. Multiple calculi were present. On histology, thickened area showed sheets and nests of moulded small cells with hyperchromatic nuclei, brisk mitotic activity and confluent necrosis. A diagnosis of small-cell NEC is established, and confirmed by positive immunoreactivity to neuroendocrine markers (CD56, Synaptophysin) and epithelial markers (CK7 and CAM5.2). Multiple foci of high-grade BilIN were noted. Subsequent entire submission of the gallbladder revealed no adenocarcinoma present. The pathologic stage was pT2a pNX. Conclusion In conclusion, this rare gallbladder carcinoma is found incidentally in a patient with acute cholecystitis symptoms and no clinical proof of mass lesion. In addition, there is a background of high-grade BilIN, which shares the molecular pathway of small-cell NEC. Therefore, awareness of such coexistence of these two pathologic entities in the same gallbladder, is essential to alert pathologists to look for the poorly-prognosis small cell NEC, whenever BilIN is encountered in random section of a gallbladder.