通常腺腫とcolitic cancer/dysplasiaの鑑別―生検を含む

Differential Diagnosis between Sporadic-type Adenoma and Colitic Cancer/Dysplasia in Ulcerative Colitis

要旨　潰瘍性大腸炎（UC）のdysplasiaはcolitic cancerに進展していくリスクの高い前癌病変であるため，多くは全大腸切除の適応である．内視鏡的に認知できる隆起を伴ったdysplasiaはdysplasia-associated lesion or mass（DALM）と呼ばれており，特に初回検査で診断された症例はlow grade dysplasiaであっても浸潤癌を合併していることがある．DALMの多くは不整な粗大顆粒状あるいは絨毛様の板状隆起を呈する境界不明瞭な病変（non-adenoma-like DALM）であり，典型例での診断は比較的容易である．しかし，なかには腺腫様のDALM（adenoma-like DALM；Ad-DALM）も認められ，同じくUC患者に発生するsporadic-type adenoma（UC-SpAd）との鑑別が問題となる．UCの内視鏡的・組織学的罹患範囲外に発生した境界明瞭な病変はUC・SpAdと診断してよいが，罹患範囲内に発生したpolypoid dysplastic lesionについては，その周囲に平坦なdysplasiaや癌が証明されない限りAd-DALMと確定診断することはできない（indeterminate lesion）．厳密な鑑別はできないが，UC発症から10年以上経過している50歳未満の患者で，DALMに特徴的ないくつかの組織学的所見とp53強陽性・β-catenin陰性の所見を有するものはprobable Ad-DALMに分類して外科的対応を検討する．UC-SpAdとprobable UC-SpAdはfree marginが確保されていれば一般患者の腺腫と同様の対応が可能であるので，DALMの一部でないことを確認するための病変周辺からの複数個生検が重要な意味を持つ．

　Dysplasia occurring in ulcerative colitis (UC) is a precancerous lesion requiring colectomy. The macroscopically visible lesions are designated as dysplasia-associated lesions or masses (DALMs) and often complicate invasive carcinomas particularly in patients with DALMs found at the first endoscopy. Non-adenoma-like DALM usually shows an irregular protuberant or villous plaque with an ill-defined edge, and the gross appearance is distinct from sporadic-type adenoma in UC (UC-SpAd) . One specific subtype of DALM is an adenoma-like lesion (Ad-DALM) resembling UC-SpAd. Histological criteria for Ad-DALM is that the lesion has developed within an area of colitis and associated flat dysplasia or a carcinoma detected during follow-up evaluation, while the well-circumscribed lesion found outside the colitis area is diagnosed as UC-SpAd. To choose an appropriate therapeutic strategy, the indeterminate lesion should be classified into probable Ad-DALM or probable UC-SpAd after considering clinical and pathological findings. At present, the features suggesting Ad-DALM are the patient's age (less than 50 years), duration of UC (more than 10 years), strong staining with p53, and negative staining with β-catenin as well as characteristic histology. In probable UC-SpAd, which may be treated with polypectomy, it is particularly important to keep a free margin and to obtain additional biopsy specimens from the surrounding flat mucosa to determine whether the polypoid lesion is part of the dysplasia.