粘膜下腫瘍様の形態を示した食道表在癌―臨床および画像的特徴，鑑別診断

Superficial Esophageal Cancer with Appearance of Submucosal Tumor―Clinical and Endoscopic Characteristics

要旨　上皮下に腫瘍があり，癌巣の表面を正常上皮が覆っている粘膜下腫瘍様の形態を示す食道癌は，表面に露出している癌巣部分が少ないため，早期癌の段階で発見することは困難であり，発見時点で既に粘膜下層以深に進行していることが多い．粘膜下腫瘍を示す食道癌には，低分化型扁平上皮癌も含まれるが，その大半は，特殊な組織型の癌であり，未分化癌，類基底細胞癌，腺様囊胞癌，腺扁平上皮癌，粘表皮癌などが挙げられる．これらの癌を鑑別するには，①隆起の形(隆起の丈と基部の広さ)，②周囲粘膜からの立ち上がり，③表面の凹凸や表面性状，④上皮内伸展の有無に注目する．未分化癌と腺様囊胞癌は，隆起の立ち上がりが急峻で，隆起の丈が高い0-Ipl型に対し，類基底細胞癌は，立ち上がりなだらかで丈の低い0-Isep型か，隆起の丈が高く，基部が狭い0-Ip型を示していた．表面の結節状の凹凸は，腺様囊胞癌が最も目立ち，未分化癌，類基底細胞癌と順に凹凸が目立たなくなっていた．未分化癌はしばしば上皮内伸展を伴い，類基底細胞癌では，隆起の頂上に扁平上皮癌を伴うことが多い．腺扁平上皮癌は，陥凹が主体の0-IIc型病変であった．粘膜下腫瘍様の形態を示す，特殊な組織型の食道癌は，リンパ行性や血行性の転移が早く，扁平上皮癌に比べ予後が悪いため，治療方針を決定するためにも，治療前の組織学的診断が不可欠である．

　Some superficial esophageal cancers are observed as protruding lesions, covered by esophageal mucosa and look like submucosal tumors. The tumor tissue occupies the subepithelial layer and cancer invasion frequently reaches is still the submucosa. Their early detection and differential diagnosis are difficult. Many pathological studies concerning them have revealed that particular histological types are frequently noted among them. These types are lesions such as undifferentiated carcinoma, basaloid squamous carcinoma, adenoid cystic carcinoma, adeno-squamous carcinoma, mucoepidermoid carcinoma and poorly differentiated squamous cell carcinoma. Compared with squamous cell carcinoma of the esophagus, they have malignant clinical features such as frequent lymph node metastasis and distant organ metastasis. Differential diagnosis on these cancers is essential for selection of treatment. Conventional endoscopy should be carried out observing the shape of the tumor (its height, margin, irregularities of the surface) and concomitant mucosal cancer. Protruding lesions with a wide base (type 0-Ipl) are highly likely to be undifferentiated carcinomas on adenoid cystic carcinomas. Basaloid carcinomas are identified as protruding tumors with ill-defined borders or sometimes with narrow bases (polypoid type : type 0-Ip). Protruding lesions with nodular and irregular shapes are suggestive of adenoid cystic carcinomas. These features are less prominent among undifferentiated carcinomas and basaloid carcinomas. Basaloid carcinomas frequently accompany mucosal cancers (squamous cell carcinoma) on the top of the protruded lesion. Slightly depressed types (type 0-IIc) are more common among adeno-squamous carcinomas. In order to get tumor tissues from under the esophageal mucosa, bite biopsy should be repeated at the same site of the tumor. Sometimes aspiration cytology by fine needle puncture is useful for differential diagnosis.