胃型形質の低異型度分化型胃癌の頻度と臨床病理学的特徴

The Frequency and Clinicopathological Features of Low-grade Well-differentiated Adenocarcinoma of Gastric Phenotype（LG-WDA-G）

要旨●低異型度分化型腺癌（LG-WDA-G）の頻度およびその臨床病理学的特徴を調べるため，胃癌186例202病変に対して免疫染色（MUC2，MUC5AC，MUC6，CD10）を施行し，LG-WDA-G 7病変が抽出された．LG-WDA-Gの頻度は，全胃癌中3.5%で，tub1の6.1%と低頻度であった．患者の性別，年齢，癌の発生部位や肉眼型には特徴的傾向はなかった．背景粘膜は1病変を除き中等度の腸上皮化生を伴う萎縮粘膜であった．大きさは2〜26（平均11）mm，深達度はT1a（M）6病変，T1b（SM）1病変，脈管侵襲はすべて陰性であった．組織型はすべてtub1で未分化型成分の混在はなかった．一方，高異型度分化型癌では胃型形質を有するものの，完全腸型より未分化型成分の混在頻度が高かった．LG-WDA-Gは未分化型への進展に乏しい低悪性度の癌であり，LG-WDA-Gの段階で発見すれば，内視鏡的治癒切除が可能であると考えられる．しかしながら，しばしば生検診断が困難であるため，生検診断にのみ依存することなく，臨床的特徴を十分把握して，癌の確定診断を行う必要があると思われる．

　We conducted immunohistochemical stains（MUC2, MUC5AC, MUC6 and MUC5AC）for 202 gastric cancers to investigate the frequency and clinicopathological features of LG-WDA-G（low-grade well-differentiated adenocarcinoma of gastric phenotype）. Eventually, we extracted seven cases of LG-WDA-G.

　The incidence rate of LG-WDA-G was 3.5% in all gastric cancers and 6.1% of tub1, and we observed no particular trend in the sex and age of patients and site and gross appearance of lesions. The background mucosa was atrophic with moderate intestinal metaplasia in almost all cases. The size of lesions ranged from 2 to 26mm（mean, 11mm）. Regarding the depth of invasion, six were intra-mucosal carcinomas, and the remaining one was submucosal invasive. In addition, the lymphovascular invasion was negative in all cases. Conversely, the incidence of the presence of undifferentiated components was higher in the high-grade differentiated carcinoma of gastric phenotype than that of the complete intestinal phenotype.

　LG-WDA-G is suggested to be a cancer of low-grade malignancy, and endoscopic curative resection is possible if it is detected at the stage of LG-WDA-G. Owing to the difficulty in its precise diagnosis only by biopsy, it is necessary to not only depend on the biopsy diagnosis but also make a definite diagnosis with clinical features.