Is型大腸sm癌の成り立ち―病理の立場から

Histogenesis of Large Bowel Carcinoma of the Type Is (Protruded and Sessile Type) with Submucosal Invasion

要旨　進行大腸癌の直前先行病変として注目されているIs型大腸sm癌10例〔内視鏡的摘除（endoscopic resection；ER）6例，手術4例〕をreviewし，Is型sm癌の成り立ちを考察した．これら症例はすべて最大径10mm以上であり，ER例の大きさは10～20mm（平均13mm）であるのに対し，手術例は20～30mm（平均24mm）であった．癌の組織型は，ほとんどが明らかな腺癌（超高分化癌ではない）で，深達度はsm₁3例，sm₂6例，sm₃1例であり，手術例に深い例が多かった．また，下田・池田らのpolypoid growth（PG）は，10例中9例にみられた．腺腫成分は5例（すべてER例）のみにみられたが，陰性の5例中4例はよりサイズの大きい手術例であった．したがって腺腫成分は腫瘍の増大に伴い消失するものと思われた．以上の結果から，Is型大腸sm癌は，その多くがPG由来，腺腫由来であり，non-PG由来，de novo carcinomaはあってもまれと考えられた．

　We considered the histogenesis of large bowel carcinoma of the type Is, i.e. protruded and sessile type, with submucosal invasion, which recently attracted much attention as an immediate precursor of advanced carcinoma, using 10 〔six endoscopically resected (ER) and four surgical〕 cases. All the tumors were 10 mm or more in size (largest diameter), and the ER cases, 10～20 mm (13 mm in average) were larger than those of the surgical cases, 20～30 mm (24 mm in average). Histologically, most of the tumors showed overt carcinomas of well differentiated or moderately differentiated type (not of very well differentiated type), and the invasion depths were sm1 (sm shallow) in three, sm2 (sm intermediate) in six and sm3 in one, the surgical cases having, in general, deeper invasion than the ER cases. Polypoid growth (PG) indicating the presence of intramucosal tumor growth twice or more as thick as the thickness of the surrounding uninvolved mucosa existed in nine of 10 cases. Adenomatous component was found in five of six ER cases, but in none of the surgical cases, which suggested that the adenomatous component was replaced by carcinoma as the size of the tumor increased. Thus, large bowel carcinoma of type Is with submucosal invasion may be formed mainly through PG tumor and adenoma, and only rarely through non-PG tumor and de novo carcinoma.