大腸T1癌内視鏡切除標本の正しい取り扱いと病理組織診断—SM浸潤度評価のポイントとピットフォール

Histological Evaluation of the Depth of Submucosal Invasion of pT1 Colorectal Carcinoma

要旨●SM浸潤度は粘膜筋板を基準に判定されるが，その走行が同定・推定できない病変をどのように選別するかが，浸潤度評価で最も大切なポイントである．デスミン染色でSM浸潤領域に粘膜筋板が認められた場合でも，α-SMA染色によりその周囲にdesmoplastic reactionが認められる場合は，SM浸潤度判定の再現性を担保し，過小評価を避けるため，粘膜筋板の“変形あり”として，SM浸潤度は病変表層から測定する．現行の有茎性pT1癌のSM浸潤度判定は再現性に問題があり，“頭部浸潤”と“茎部浸潤”の2分法への変更が望ましいと考えられるが，“頭部”と“茎部”の境界線の定義を明確化する必要がある．

　The essentials of the evaluation of the depth of SM（submucosal）invasion of pT1 colorectal carcinoma is the discrimination of whether or not the location of the muscularis mucosae is possible to identify or estimate. When desmoplastic reaction by α-smooth muscle actin staining is detected around the muscularis mucosae, it should be judged as that the location of muscularis mucosae is uncertain, and the depth of SM invasion should be measured from the surface of the lesion. This method ensures reproducibility in measuring the depth of SM invasion and avoids underestimation. However, this method of measuring SM invasion depth is considered inappropriate in pedunculated lesions. While the dichotomy of “head invasion” versus “stalk invasion” is becoming more accepted, there is a need for clear definition of the boundary between the “head” and “stalk”.