胃型分化型腺癌との鑑別が問題となった胃型腺腫の1例

Gastric-type Adenoma Which Resembled Differentiated Adenocarcinoma, Report of a Case

要旨　患者は45歳，女性．4年半前から胃ポリープを指摘，今回胃型腺腫の診断で内視鏡的粘膜切除術（endoscopic mucosal resection；EMR）を施行．病変は3×2.5cm大，軽度の分葉状構造を示す隆起性腫瘤．組織学的には幽門腺に類似した立方状細胞から成る腺管の増生がみられ，腺腔は延長，屈曲が著しく嚢胞状に拡張した部分を多々伴っていた．部分的には明瞭な核小体を伴う腫大した核を認め，配列にも軽度の乱れを認めた．MIB-1抗体陽性細胞は表層でごくわずか認めただけであった．以前に施行された生検組織の再検討では今回の所見とほぼ同様であり，幽門腺型胃型腺腫と診断された．これまでの胃腺腫の組織診断基準は腸型を主体としており，分化型腺癌との鑑別が重要であった．しかしながら胃型腺腫は異型の弱いその特異な組織像により，過形成性病変から分化型胃型腺癌までの幅広い鑑別が必要であると考えられた．

　A hyperplastic polyp 30 mm in size was detected in a 45-year-old woman four and a half years before endoscopic follow-up study of the gastric polyp. A biopsy study of the polyp led to the diagnosis of gastric-type adenoma. Endoscopic mucosal resection was performed. The resected specimen showed an elevated lobular tumor, 30 × 25 mm in size. Histopathologically most of the tumor was composed of cystic pits and proliferated pyloric-type glands, lined by cells identical to those of the normal gastric mucosa. The cells occasionally had swollen oval nuclei which contained one or two distinct nucleoli. Ki-67 positive cells were found only sporadically in the upper part of the tumor. Re-examination of the initial biopsy (performed on Nov. 1992) revealed gastric-type adenoma the same as the EMR specimen. Histopathological criteria of gastric adenomas have been based on intestinal-type adenomas, so, when gastric-type adenoma shows mild atypia, it is important to distinguish it from hyperplastic polyp or well differentiated adenocarcinoma.