肛門癌の病理

Clinico-pathological Aspects of Anal Cancers

　大腸癌取扱い規約によると，肛門管というのは，恥骨直腸筋付着部上縁より肛門縁までの管状部と規定されている（Fig. 1）．肛門癌はこの肛門管およびその周辺に発生した癌ということになる．

　肛門癌を述べるにあたっては，肛門管の発生と解剖を知ることが重要である．肛門は種々の上皮が入りまじっている．とくに歯状線の上方の部分はcloacaから分かれた肛門膜がその発生源で，胎生9週頃に外胚葉性の皮膚部分が挙上して生ずる重層扁平上皮層と連絡する．その長さは個人差があって一定しない．肉眼的には光沢のある微細な膜様に見える部分¹⁾²⁾で，ややうす紫色を呈し，組織学的には尿道上皮に似た移行上皮で，重層立方上皮であるが，実際にはこの部分は円柱上皮，扁平上皮なども入り組んでいる．

　Cancers growing in the anal canal and its surrounding tissue are various in their pathological types, and this is an important factor for the treatment and prognosis. Forty patients of anal cancers were treated for the past 15 years at Social Insurance Central Hospital. The incidence is 15% of anorectal cancers, which exceeds the reported incidences in other institutions.

　Histologically, there were 9 patients with tubular adenocarcinoma, 6 with papillo-tubular adenocarcinoma, 10 with colloid carcinoma, 2 with mucocellular adenocarcinoma, 6 with squamous cell carcinoma, 2 with mucoepidermoid carcinoma, 2 with basaloid carcinoma, 2 with basal cell carcinoma and 1 with extramammary Paget's disease.

　Cancers of anal gland or anal duct origin or associated with long-standing anorectal fistulas are clinicopathologically the most characteristic of malignant neoplasms arising in the anal region. Their specific features are that they grow extracanalicularly with slight or no abnormality in the anorectal mucosa.

　Most of the growths belong to mucinous type, having virtually no metastasis to the lymph nodes along the superior rectal artery, few in the inguinal nodes, with relatively good prognosis.