表在型食道扁平上皮癌，上皮内腫瘍，非腫瘍性病変の病理診断

Pathological Diagnosis of Superficial Esophageal Squamous Cell Carcinoma, Squamous Intraepithelial Neoplasia, and Non-neoplastic Lesion

要旨

表在型食道扁平上皮癌の病理診断において炎症性変化，上皮内腫瘍性病変との鑑別は治療方針に関わるため重要である。扁平上皮癌は細胞異型，構造異型，フロント（境界）形成を総合して診断される。炎症性変化など非腫瘍性病変では核腫大や細胞密度の増加などの所見を示すがフロント形成がないことを腫瘍性病変との鑑別点とし，臨床情報や内視鏡所見を併せて総合的に判断する。『食道癌取扱い規約 第12版』における上皮内腫瘍は「上皮内腫瘍性病変から癌を除いたもの」で，核異型が軽度で細胞密度が低く，表層分化傾向を示すことから診断される。定義上はWHO分類第5版におけるlow -grade squamous dysplasiaに相当するが，取扱い規約もWHO分類も定義や用語が変遷してきた歴史があり混乱しやすく，概念の理解と適切な対応が望まれる。また，非飲酒・非喫煙者に発生する表在型食道扁平上皮癌の組織像について解説する。

　The differential diagnosis of superficial squamous cell carcinoma includes squamous intraepithelial neoplasia and reactive changes such as inflammatory changes and is essential for the appropriate treatment for each disease. Squamous intraepithelial neoplasia can be diagnosed based on the findings of cytological and architectural atypia and abrupt transition between neoplastic and adjacent nonneoplastic areas. Reactive changes such as inflammatory changes also show cytological and architectural atypia. However, the finding of no abrupt transition between an atypical and an adjacent nonatypical area as well as review of clinical information and endoscopic findings can provide an important clue in the differential diagnosis between intraepithelial neoplasia and reactive changes. Squamous intraepithelial neoplasia is defined as an intraepithelial lesion regarded as a neoplastic process excluding an obvious cancerous lesion, according to the Japanese Classification of Esophageal Cancer, 11th edition. From the viewpoint of the Japanese classification, squamous intraepithelial neoplasia is histologically characterized by mild cellular atypia, low cellularity, and involvement of the lower half of the epithelium, the findings of which are consistent with low grade squamous dysplasia by the WHO classification, fifth edition. Several changes over the years in the definition and terminology of intraepithelial neoplasia/dysplasia in both the Japanese and WHO classifications caused confusion regarding the concept of intraepithelial neoplasia/dysplasia among clinicians and pathologists. A proper understanding of intraepithelial neoplasia/dysplasia is required for a clinical decision and for adequate treatment. Finally, histopathological features of superficial esophageal squamous cell carcinoma in patients without a history of smoking and alcohol consumption is also described in this article.