炎症性腸疾患関連腫瘍の病理診断

Pathological Diagnosis of IBD-associated Dysplasia/Cancer

要旨●炎症性腸疾患（IBD）である潰瘍性大腸炎（UC）やCrohn病（CD）を背景に発生する消化管腫瘍は，通常の散発性腫瘍とは発癌経路や臨床病理像が異なることが知られ，新WHO分類では“IBD-associated dysplasia”として取り上げられている．本稿では，2024年に出版された「炎症性腸疾患関連消化管腫瘍診療ガイドライン」を踏まえ，IBD関連腸腫瘍の用語定義や病理学的診断基準について概説する．また，潰瘍性大腸炎関連腫瘍（UCAN）に特徴的な肉眼形態や組織像についても解説するとともに，UC関連dysplasiaと散発性腺腫との鑑別やUCANの発生母地となりうるSEC（serrated epithelial change）についても考えてみたい．

　Intestinal epithelial neoplasia arising in inflammatory bowel disease（IBD）, including ulcerative colitis（UC）and Crohn's disease, exhibits carcinogenetic pathways and clinicopathologic features distinct from conventional sporadic epithelial neoplasia. In the latest World Health Organization classification, these intramucosal lesions are categorized as “IBD-associated dysplasia.” Here, we provide an overview of the terminology and pathological diagnostic criteria of IBD-associated intestinal neoplasia, considering the 2024 Japanese Society for Cancer of the Colon and Rectum Guidelines for the Clinical Practice of Inflammatory Bowel Disease-Associated Intestinal Neoplasia. Furthermore, we describe the macroscopic and histological features of UC-associated dysplasia/cancer. We also discuss the differential diagnosis between UC-associated dysplasia and sporadic adenoma, as well as the concept of “serrated epithelial change,” which can serve as a precursor lesion for UC-associated dysplasia.