Helicobacter pylori陰性未分化型胃癌の側方進展診断におけるNBI併用拡大観察

Magnifying Narrow Band Imaging for Determining the Lateral Extent of Helicobacter pylori-Negative Undifferentiated Gastric Cancer

要旨　Helicobacter pylori（HP）感染率の低下による胃癌発生率低下の時代が到来しつつある．しかし，まれにHP未感染の非萎縮粘膜にも胃癌を認めることがあり，その胃癌には未分化型胃癌が多い．今回はHP陰性未分化型胃癌の側方進展診断におけるNBI併用拡大観察（M-NBI）の診断能を検討した．ESDを施行した未分化型胃癌においては，HP未感染の割合は15.2％と低く，かつM-NBIの側方範囲診断は不良であった．未分化型胃癌全体における白色光通常観察（C-WLI）ならびにM-NBIの側方範囲診断能には有意差がなく，さらにC-WLIに対するM-NBIの上乗せ効果も認めなかった．ともに周囲粘膜との色調差の小さい病変での誤診が多かった．また，粘膜中層から深層を這うような浸潤形式でも注意が必要である．未分化型胃癌の側方進展診断においては，C-WLIを重視し，いわゆる周囲生検を行うことが必須である．

　The prevalence of gastric cancer diminishes with an increase in the rate of Helicobacter pylori（HP）infection. However, the risk of gastric cancer remains in patients without HP infection. Histopathologically, undifferentiated gastric cancer is dominant in HP-negative cases. In this study, we retrospectively investigated the diagnostic performance of M-NBI（magnifying narrow band imaging）for determining the lateral extent of HP-negative, undifferentiated gastric cancer. The prevalence of HP-negative cancer was low（15.2%）among all cases of undifferentiated gastric cancers resected by endoscopic submucosal dissection. The diagnostic accuracy of M-NBI in determining the lateral extent of HP-negative, undifferentiated gastric cancer was inadequate and did not differ from that of C-WLI（conventional white light imaging）. Therefore, M-NBI did not offer an additional advantage when the tumor margins were not identified by C-WLI. In particular, the lateral extent was difficult to diagnose because of very subtle color differences or because of the presence of developing cancer cells in the intermediate and/or deep mucosal layers as observed by histopathological examination. In cases of undifferentiated gastric cancer, multiple biopsy specimens should be obtained from the surrounding mucosa.