To investigate the characteristics of superficial type colorectal epithelial neoplasia (SN) (adenoma, SAd; adenocarcinoma, SCa; superficial-elevation type, E; superficial-depression type, D), the expression of Lewis y (Le(Y)), a marker of apoptosis, and the labeling index of proliferative cell nuclear antigen staining (PCNA-LI) in the intramucosal regions of 56 SN lesions were investigated. Expression of Le(Y) was observed in cytoplasm or cell membrane from the surface to deep within some tubules in SN lesions. Le(Y) was detected at higher rates in SCa lesions than in SAd lesions, in SCa lesions greater than 11 mm in diameter than in those less than 10 mm in diameter, in SCa-E lesions than in SCa-D lesions, in SCa lesions deeper than middle third of the submucosal layer, and was not related to size or macroscopical appearance of SAd lesions. PCNA-LI rate was higher in SCa lesions than in SAd lesions, in SCa lesions with carcinoma invasion to the submucosal layer than in SCa lesions with carcinoma invasion limited to the propria mucosa, and that of SAd lesions was inversely correlated with tumor size although that of SCa lesions was positively correlated with tumor size. There was a relationship between the high degree of expression of Le(Y) and PCNA-LI. In SCa lesions apoptosis and cell proliferation reflected that the enlargement and/or deeper invasion of carcinomatous tissue and in SAd lesions apoptosis had no relationship to tumor size although the cell proliferation inversely correlated with tumor size. This suggested that SCa-D lesions and the SCa-E with much higher proportions of apoptotic cells progressed to the ulcerative advanced cancer, and the size of many SAd lesions had a limit.

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