肛門部悪性腫瘍の検討―特にbasaloid carcinomaについての考察

Histopathological Studies of Anal Malignancies with Special Reference to Basaloid Carcinoma

　肛門部とは肛門管と肛門周囲皮膚をさし，この部の悪性腫瘍は比較的少ない．その上，肛門管の複雑な組織解剖学的構造を背景として，これより発生する腫瘍が病理形態学的に多様であり，その発生母地について解明すべき点が多い．そこでわれわれは過去約22年間に東大付属病院で切除された肛門部悪性腫瘍症例の病理組織学的特徴を調べ，また特に現在種々の見解がとられている，いわゆるbasaloid carcinomaおよびその発生母地と関連があるといわれている肛門管移行帯上皮¹⁾について若干の考察を行った．

材料および方法

　1955年6月から1976年末までの約22年間に当院病理部で取り扱った肛門部悪性腫瘍，すなわち肛門管および肛門周囲皮膚に主座し，この部から発生したと考えられる悪性腫瘍の手術材料を検討対象とした．ただし肛門管の直腸型¹⁾と考えられる癌は，肛門管直腸粘膜部に発生したものか，または直腸膨大部に発生し，これが肛門管に波及したものか，その判定がきわめて困難であること，また組織発生学上，直腸型癌は直腸膨大部に発生した癌と何ら変わるところがないことなどの理由で今回の検討対象から除外した．

　The purpose of this paper is to describe histopathology of 18 cases of malignant tumors of the anal region, excluding adenocarcinoma of the rectal type, seen at Tokyo University Hospital during the years 1955～76.

　The following histopathological types were classified: adenocarcinoma probably arising from the anal glands (3 cases), adenocarcinoma associated with anal fistula (1), squamous cell carcinoma (6), basaloid carcinoma (5), adenoacanthoma (1), malignant melanoma (1), and basal cell carcinoma of the perianal skin (1).

　Five cases of basaloid carcinoma of the anal canal in particular are extensively discussed. Although various diagnostic terms, such as transitional cloacogenic, basosquamous, undifferentiated and others, have been used by different investigators to describe the similar lesions, we prefer the term, basaloid carcinoma, to others because of its purely descriptive nature and expression of histological characteristics. Basaloid carcinomas resemble basal cell carcinoma of the skin, especially in that palisading of the nuclei at the periphery of the tumor cell nests is present.

　While basaloid carcinoma is predominantly basaloid, sharply difined pearls of keratin are occasionally demonstrated. In our experience there are at times small foci of basaloid structure in other squamous cell carcinomas of the anal canal as well as esophagus.

　We consider that basaloid carcinoma of the anal canal is not a strictly independent type, but a variation of squamous cell carcinoma.