1）病理診断─診断基準

Pathological Diagnosis of Colorectal Epithelial Tumors

要旨　大腸上皮性腫瘍は，一般的にはその異型度により低異型度（軽度異型，中等度異型）と高異型度（高度異型）に分類されるが，欧米の基準における高異型度（高度異型）は本邦においては高分化腺癌と診断される．細胞異型は癌相当であっても，粘膜内病変は転移を来さないため過剰治療（外科的腸管切除）を避けるために，欧米では“癌”と診断されない．ただしWHO分類ではこの矛盾の解消のため“carcinoma in situ”という用語を用いるように推奨している．診断基準は，欧米と本邦の間だけでなく，国内の病理医間でも完全には一致しない．診療において最も重要なことは，病理診断名を付けることより治療方針決定に有用な情報を与えることである．すなわち，粘膜内病変に関しては浸潤癌への進展の危険性のある病変かどうかの判定，粘膜下層へ進展した病変では癌性浸潤か偽浸潤かの判定とリンパ節転移の危険性の評価である．そして病理医側の対応としては，診断の違いの幅が臨床的治療方針に対応した幅に収まる程度には一致するよう精度を上げる必要がある．また，生検診断における誤診を避けるためには，病理組織学的に良悪性の誤診の危険性がある病変の存在を，病理医のみならず臨床医も知っておくことも必要である．

　Intraepithelial neoplasias of the large intestine are generally classified into low-grade and high grade, but the high-grade in Western countries is diagnosed in Japan as well differentiated adenocarcinoma. It is not diagnosed as“carcinoma”in Western countries to avoid overtreatment（surgical colorectal resection）because intramucosal carcinomas do not give rise to metastasis even if the cellular atypia is equivalent to that of carcinoma. However, it is recommended to use the WHO classification term“carcinoma in situ”in order to remove this apparent contradiction.

　Lack of complete agreement between Japanese and Western pathologists concerning the diagnostic criteria for these colorectal epithelial tumors is reflected in the fact that there is a lack of agreement even among Japanese pathologists themselves.

　What is most important clinically is to obtain information that is useful for treatment rather than to make a pathological diagnosis. Pathologists should inform clinicians of the risk of development of invasive cancer or of the possibility of lymph node metastasis. It is necessary for pathologists to minimize the range of difference in the diagnostic criteria, so that the clinical treatment guidelines can be applied more effectively. In addition clinicians should be aware of the difficulties in making pathologic diagnosis, and pathologists therefore should be aware of this.