Intracholecystic Papillary Neoplasm With Associated Invasive Carcinoma, Accompanied by Tumor Thrombi of Hepatoid Adenocarcinoma: A Case Report.

Hepatoid adenocarcinoma (HAC) is a rare extrahepatic adenocarcinoma characterized by hepatocellular differentiation. HAC arising in the gallbladder is rare. We report a case of intracholecystic papillary neoplasm (ICPN) with HAC, most of which were tumor thrombi. The patient was a 78-year-old Japanese woman diagnosed with a gallbladder mass, detected by ultrasonography. She underwent cholecystectomy with lymph node dissection. Histopathological examination revealed exophytic papillary growth consistent with ICPN with associated invasive carcinoma. Notably, many tumor nests displayed characteristics of HAC, including eosinophilic granular cytoplasm and solid trabecular patterns. Immunohistochemically, tumor cells were positive for AFP, Glypican 3, and Hep Par 1 but negative for SALL4. Our findings underscore the importance of recognizing HAC components in gallbladder lesions, particularly in the context of ICPN with associated invasive carcinoma, as they may significantly impact patient prognosis.