Hepatocellular carcinoma with mesothelioma-like dissemination

Reported herein is a case of hepatocellular carcinoma (HCC) with unusual peritoneal dissemination masquerading as peritoneal mesothelioma. A 61-year-old man was clinically found to have multiple tumors in his abdominal cavity; peritonitis carcinomatosa was suspected. An autopsy revealed numerous tumors of various sizes in the abdominal serosa, omentum, and diaphragm. No signs of tumor, fibrosis, or cirrhosis were found in the liver, except for a small nodule in the hepatic triangular ligament. Histologically, the tumor cells proliferated in thick trabeculae or in sheets and formed a few canaliculi and tubules with homogenously brown contents in their lumina, which stained positively with Hall stain. Immunohistochemically, these tumors were positive for hepatocyte, alpha-fetoprotein (AFP) and low-molecular-weight cytokeratin; were focally positive for pan-cytokeratin and epithelial membrane antigen (EMA); and were negative for high-molecular-weight cytokeratin, vimentin, and calretinin. Carcinoembryonic antigen (CEA) produced a bile canalicular immunohistochemical staining pattern. Thus, the tumor was diagnosed as an HCC (Edmondson II type) of the triangular ligament with massive peritoneal dissemination. The origin of this tumor and its differential diagnosis (malignant mesothelioma, hepatoid adenocarcinoma, and hepatoid yolk sac tumor) are discussed.