Few cases of gastric carcinoma with infiltrating multi-nucleated giant cells (MGCs) have been reported, and giant cells infiltrating the gastric carcinoma were previously described as osteoclast-like giant cells (OGCs). However, hepatoid adenocarcinomas have never been reported previously, and the present case is extremely rare. A 100-year-old Japanese man with gastralgia was found to have a mass in his gastric body. Histological examination showed a poorly differentiated adenocarcinoma with infiltration of MGCs. Vascular and lymphatic invasion were noted but there were no metastases. Almost all the tumor comprised cells with hepatoid-like features. The MGCs proliferated, with infiltration of lymphoid cells. A few MGCs contained mucous material in their cytoplasm, indicating these were foreign-body giant cells. Immunohistochemically, the hepatoid-like components were positive for AFP, and staining with polyclonal antibodies against carcinoembryonic antigen (CEA) showed the canalicular pattern. We concluded that this component was hepatoid adenocarcinoma. The MGCs were positive for CD68, and surrounding infiltrating lymphoid cells were diffusely positive for CD3. Infiltration of MGCs in gastric cancer may represent a cellular immune response against gastric cancer invasion. Further studies are required to elucidate the etiology of MGCs in gastric cancer.
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