腸上皮化生のない背景粘膜から発生した胃癌の臨床病理学的特徴―特にHelicobacter pylori感染との関連について

Gastric Carcinoma Arising from Mucosa with no Intestinal Metaplasia―Its Clinicopathological Features in Association with Helicobacter pylori (Hp)

要旨　一般的には，Helicobacter pylori(Hp)感染により慢性萎縮性胃炎（腸上皮化生）を経て分化型腺癌が発生することが言われている．われわれの以前の研究で，若年者胃癌ではHp感染はあるが腸上皮化生を認めない粘膜から低分化腺癌が発生する発癌経路が示唆された．今回は背景粘膜に注目し腸上皮化生を認めない胃粘膜に発生した胃癌〔IM(－)胃癌〕40例の臨床病理学的特徴とHp感染の関連に関して検討した．IM(－)胃癌は臨床病理学的に，女性にやや多く，胃体部発生が多く，組織型はほとんどが低分化腺癌であるという若年者胃癌に類似した特徴を有していたが，免疫染色によるHp陽性率は62.5％で比較的高率であったが，若年者胃癌のそれ(96％)より低率であった．IM(－)胃癌の中でHp感染陽性群と陰性群では，陰性群で慢性活動性胃炎の程度が軽度である傾向があったが，その他の臨床病理学的因子に差異は認められなかった．Hp感染による慢性萎縮性胃炎(腸上皮化生)を経て癌化する経路以外に，慢性活動性炎症が直接発癌に関与する経路が存在し，特に後者は低分化腺癌の発生経路として重要であると思われる．また，一部ではあるがHp感染や慢性活動性胃炎と無関係に発生するものも存在することが示唆された．今後はHp感染陰性胃癌の増加が予想され，これらの癌化の機序に注目する必要がある．

　It is generally said that differentiated-type adenocarcinomas of the stomach arise from the mucosa with intestinal metaplasia associated with chronic atrophic gastritis due to Helicobacter pylori (Hp) infection. Our previous study revealed that almost all undifferentiated-type adenocarcinoma in young patients (under 30) arose from mucosa with no intestinal metaplasia in spite of the high frequency of Hp infection. In this study, we selected 40 cases of IM (－) GC (gastric cancer arising from the mucosa with no intestinal metaplasia), and reviewed their clinicopathological features in association with Hp infection. IM (－) GC was more frequently present in females in the gastric body. Histologically, almost all lesions were undifferentiated adenocarcinomas. These features were similar to those of young patients, but the incidence of Hp infection indicated by immunohistochemical stain is lower in cases of IM (－) GC (62.5％) than in young patients (96％). The degree of chronic active gastritis was milder in the group with Hp infection (－) than in that of Hp infection (＋). Other clinicopathological factors didn't differ between these two groups.

　Except for the carcinogenetic pathway based on Hp infection-chronic atrophic gastritis-intestinal metaplasia sequence, the existence of a pathway directly associated with inflammation due to Hp infection is suggested. The latter is considered to play an important role for carcinogenesis of undifferentiated adenocarcinoma of the stomach. In addition, another minor pathway is also suggested to exist with no relation to Hp infection or chronic active gastritis. Gastric carcinoma with no Hp infection is expected to increase in the near future, and it is necessary to pay attention to the carcinogenetic mechanism of such carcinoma.