胃癌sm浸潤の判定と深達度sm1の考え方

Assessment of Submucosal Invasion in Gastric Cancer―Therapeutic Consideration for Minimal Submucosal Invasion (sm1)

要旨　sm癌は，癌の浸潤が粘膜筋板を越えていることが必須条件となるが，粘膜筋板の確認が難しい場合はsm浸潤の判断はしばしば困難となる．その際，癌巣内あるいは癌隣接部位における直径100μm以上の小動脈の存在は，sm浸潤を強く示唆する有用な所見である．粘膜筋板が途切れているリンパ濾胞内への浸潤は，周囲の筋板との位置関係によって決定する．癌細胞を含まない粘液結節も癌の一部とみなし，その位置により決定する．判断困難な場合は，積極的に深切りを行って検証する必要がある．また，今日では，深達度smはsm_1～3と3分される傾向にあるが，sm₁の定義は，内視鏡的粘膜切除術（EMR）で根治できる深達度，すなわちリンパ節転移の危険のほとんどない深達度とすべきである．分化型癌については，粘膜筋板の下端から300μmまで，とするのが適当と考える．未分化型癌については，現時点では，このような設定を行うのは困難であり，sm浸潤例はすべてリンパ節郭清を含めた手術を行うべきであろう．

　In diagnosis of carcinoma with submucosal invasion, it is essential to confirm cancer cells or nests infiltrating beyond the lamina muscularis mucosae (m.m.). However, its judgment is sometimes difficult in examination of EMR materials, because of direction of cutting and/or artificially or pathologically disorganized m.m. In such cases, the existence of cancer cells or nests around or by arterioles larger than 100 μm in diameter suggests strongly the submucosal invasion. In case where a carcinoma falls into a lymph follicle in which the m.m. is usually lacking, the invasion depth is decided by a reference m.m. estimated from levels of m.m. existing in both sides of the follicle. A mucus nodule without cancer cells or nests should be considered as a part of carcinoma. When it exists in the submucosal layer, a diagnosis of submucosal invasion should be given.

　In these days, submucosal invasion of carcionma has been divided into three according to grade of invasion depth: sm₁, sm₂ and sm₃. From a standpoint of EMR treatment, the invasion depth sm₁ should be properly defined as a depth unassociated with lymph node metastasis. For carcinomas of differentiated type, a range 300 μm from the lowest line of the m.m. corresponded to above mentioned sm₁, which is well comparable with that for colorectal carcinomas. However, in case of undifferentiated type carcinomas, such sm₁ as to be cured by EMR could not be set because of a risk of lymph node metastasis.