臨床病理学的観点からみた大腸癌の発生・発育過程とその特徴―大腸癌の発生における腺腫の癌化（adenoma-carcinomasequence）とde novo発癌

Adenoma-Carcinoma Sequence and De Novo Cancer Theory for the Carcinogenesis in Colorectal Carcinomas

要旨　大腸癌の組織発生については，最初に腺腫が発生し，腺腫の大きさの増大に伴い，腺腫内に癌が発生するというadenoma-carcinoma sequenceと，腺腫を介さず正常大腸粘膜から直接癌が発生するde novo癌説が考えられている．現在，国際的にはadenoma-carcinoma sequenceが一般に認められている．一方，日本においては1990年前後から平坦な表面型早期癌，なかでも表面陥凹型癌が数多く発見されるようになり，それらの癌には腺腫性分を伴わない病変が多いことから，de novo癌も存在する，と認識されるようになってきている．今後，腺腫と癌に関する本邦と欧米の病理医間での組織診断基準の違いが統一され，表面型早期大腸癌の存在，その頻度が国際的に明らかにされることで，大腸癌の組織発生のメインルートが明らかになると思われる．

　There are two theories for the carcinogenesis of the colorectal carcinomas. The one is adenoma-carcinoma sequence that all the colorectal carcinoma is arose from benign adenomas and the other is de novo cancer theory that the most colorectal carcinomas arose from normal colonic mucosa not via adenomas. Adenoma-carcinoma sequence is currently recognized true as a carcinogenesis of the colorectal carcinomas, internationally. On the other hand, many flat and depressed early colorectal carcinomas have been detected in Japan from around 1990. There is no concomitant adenoma component in flat and depressed type early carcinomas so that the most flat and depressed type early carcinomas are thought as de novo cancers in Japan. In order to elucidate whether adenoma-carcinoma sequence or de novo cancer theory is the main route of carcinogenesis in colorectal carcinomas, there will be required that histopathological criterion for the diagnosis of adenoma and adenocarcinoma between Japanese and western pathologists is standardized and recognition and the incidence of flat and depressed type early carcinomas is internationally revealed.