S5755 A 2-Faced Malignancy: Hepatoid Adenocarcinoma in the Gastroesophageal Junction

Introduction: Hepatoid adenocarcinoma (HAC) is a rare variant of extrahepatic malignancy that is known to present a diagnostic challenge. It morphologically resembles hepatocellular carcinoma (HCC) and can produce alpha fetoprotein (AFP). The prognosis of such a malignancy is poor and therapeutic options are limited. We present a case of a 59-year-old man who presented with abdominal distension, jaundice, and hematochezia who was found to have hepatoid adenocarcinoma in the gastroesophageal junction (GEJ). Case Description/Methods: A 59-year-old man with a history of hypertension, coronary artery disease, and cirrhosis who was admitted due to abdominal distension, jaundice, and hematochezia. Vital signs were stable on admission. A CT of the abdomen revealed diffuse hepatic lesions suspicious for HCC and enlarged upper mediastinal and abdominal lymph nodes. Serum AFP levels were 44265 ng/ml. Endoscopic evaluation revealed bleeding internal hemorrhoids, and a medium-sized, ulcerating mass just distal to the GEJ. Biopsy of the mass resulted in adenocarcinoma with stains positive for AFP and CDX2 and negative hepatocyte specific antigen and arginase-1. AFP positive stain is suggestive of enteroblastic and hepatoid differentiation. The liver lesions were then biopsied and the findings also supported the diagnosis of HAC. The patient has finished 12 cycles of FOLFOX chemotherapy and is currently on maintenance therapy of 5-fluorouracil and leucovorin with adequate tolerance. Discussion: This case highlights the importance of recognizing such malignancies with comprehensive workup to establish diagnosis. HAC most commonly occurs in the stomach, with an incidence of around 0.3%-1% among all gastric adenocarcinomas. Middle-aged males are more commonly affected, with age difficult to estimate given its rarity. Prognosis is poor with median survival of 5-11 months and 5-year survival of 9%. It is often misdiagnosed as HCC due to close histopathological similarity. This makes immunohistochemistry crucial, with HAC commonly having positive AFP, glypican-3, and spalt-like transcription factor 4. Usage of other markers such as Hep Par 1 and arginase-1, which are more likely to be positive in HCC, can also aid in diagnosis. It is also recommended to biopsy areas of metastases for comparison, with the most common sites being the lymph nodes or liver. Treatment is largely limited to surgical resection with adjuvant chemotherapy, although rarely curative, with no evidence supporting radiotherapy or immunotherapy.