Is型大腸sm癌の成り立ち―X線の立場から

Development of Type Is Carcinomas in Colorectal Submucosal Invasive Cancer, from a Radiologic Viewpoint

要旨　無茎性早期大腸癌231病変を対象とし，Is型とⅡa型の分類の定義を行いその妥当性について検討した．まず，手術例68病変（m：12，sm：56）について検討を行い，由来肉眼型を考慮に入れ病理学的扁平率（病変の高さ/最大径）20％を超えるものはIs型，20％以下はⅡa型と定義した．この定義は，sm₂までは由来肉眼型とよく相関した．この扁平率は，X線扁平率（側面像による高さ/正面像による最大径）とも極めてよく相関し臨床的に応用可能であった．この判定基準を用い無茎性早期大腸癌231病変をIsとⅡaに分類し，臨床病理学的な相違を比較した．病変の内訳は，Is183病変（m：104，sm：79），Ⅱa48病変（m：21，sm：27）であった．ⅡaはIsに比し小さくかつsm高度浸潤例が多く，悪性度が高い病変と考えられた．陥凹を伴う病変は，Ⅱaではm癌からみられたが，Isではすべてsm₂以深の浸潤癌であった．また，浸潤度による腺腫成分の有無の比較から，Isは主にadenoma-carcinoma sequenceの発育を，Ⅱaはde novo cancerの発育進展をする可能性が示唆された．以上のように，定義によるIs型とⅡa型を浸潤度別に比較検討してみると，両者には臨床病理学的な相違がみられ，無茎性隆起型癌は発育・進展を考慮する意味でX線で計測可能な扁平率20％で分類する意義は十分にあると考えられた．

　We classified 231 sessile elevated lesions of early colorectal cancers, including elevated lesions with central depression, into two types of Is and Ⅱa according to our criteria and compared clinicopathological differences between the two types. Initially, from the results of primary analysis of 68 operated cases, we defined Is and Ⅱa type carcinomas by considering their types of origin in intramucosal cancers as follows; Lesions of which the pathological flat rate (height/size of the lesion in resected specimen×100%: PFR) was over 20% were Is type, and the others were Ⅱa type. Then, according to this definition, we determined the type of cancers which were to be treated endoscopically from the radiologic flat rate (height of lateral view/size of enface view of the lesion by barium enema×100% RFR) instead of PFR, because RFR was almost identical with PFR in the primary analysis. Of 231 lesions, Is were 183 (m: 104, sm: 79) and Ⅱa were 48 (m: 21, sm: 27). Size of Ⅱa, according to the degree of invasion, was smaller than that of Is. However, the frequency of sm₂ and sm₃ invasive cancers in Ⅱa was higher than that of Is. Ⅱa cancers with depression were regarded to develop from intramucosal cancers to sm₃ invasive cancers. However, Is cancers with depression were recognized to be sm₂, and sm₃ invasive cancers.

　From the comparison of adenomatous components in cancers according to the degree of invasion, it was speculated that Is grew mainly through the root of the adenoma-carcinoma sequence, and that Ⅱa grew mainly through the root of the de novo cancer. Thus, it is considered that our classification of Is and Ⅱa is significant in respect to the development of sessiled elevated lesions of early colorectal cancers from the clinicopathological difference between the two types.