4）肝様腺癌

Hepatoid Adenocarcinoma─A Spefical Histological Type of Gastric Carcinoma

要旨　肝様腺癌（hepatoid adenocarcinoma）は，肝癌類似の組織像を呈する特殊な胃癌であり，頻度は低いが高度に静脈浸潤を来し，極めて予後不良な組織型の1つである．組織学的特徴は，好酸性から淡明で豊富な細胞質を有する癌細胞が索状構造を取りながら充実性に増殖し，しばしば硝子球（hyaline globule）や細管構造（canalicular structure）がみられる．そして，免疫染色によるAFP陽性またはin situ hybridization法によるアルブミンのmRNAの検出により肝様腺癌と確定される．肝様腺癌にはAFP産生胃癌も含まれるがAFP非産生胃癌も存在し，AFP産生胃癌には肝様腺癌も含まれるが非肝様腺癌も含まれる．これらの関係は十分理解されておらず，AFP産生胃癌における肝様腺癌と非肝様腺癌の関係や，組織発生から肝様腺癌へと進展する機構の解析はいまだ不十分である．今後は組織像の詳細な評価を基礎として，それらの解析を進めていく必要がある．

　The hepatoid adenocarcinoma is one of the special types of gastric carcinoma, which resembles a hepatoma. Its incidence is low, however, its prognosis is very poor with high incidence of venous invasion.

　Histologically, the carcinoma cells have abundant eosinophilic or clear cytoplasms and grow in solid nests or sheets with a trabecular structure, occasionally accompanied by hyaline globules and a canalicular structure. The diagnosis of hepatoid adenocarcinoma can be confirmed by AFP（＋）or in situ hybridization for mRNA of albumin.

　Although the hepatoid adenocarcinoma includes both AFP（＋）and（－）oens and the AFP（＋）adenocarcinoma includes both hepatoid and non-hepatoid ones, the relation between the hepatoid and AFP（＋）adenocarcinomas is not well identified. In addition, the histogenesis and progressive mechanism of the hepatoid adenocarcinoma are also uncertain. Further analysis for them should be carried out on the basis of detailed histological evaluation.