Re-evaluation of Phenotypic Expression in Differentiated-type Early Adenocarcinoma of the Stomach

A total of 313 cases of differentiated-type early gastric adenocarcinomas, including 113 cases of small-sized carcinoma (5< × ≤10 mm) and 121 cases of microcarcinoma (0< × ≤5 mm), were examined immunohistochemically to clarify the phenotypic expressions. They were classified into four categories (gastric phenotype (G-type), intestinal phenotype, gastrointestinal phenotype, and null phenotype) by a two-step process: the phenotype based on an immunoprofile of mucin core proteins (MUCs) with CDX2 (w/.CDX2-assessment); and the phenotype of MUCs only (w/o.CDX2-assessment). CDX2 expression was observed in 89.1% (279/313); it was highly expressed in 87.6% (106/121) of microcarcinomas. MUC2 expression increased as tumor size increased (P < 0.05). Compared with w/o.CDX2-assessment, w/.CDX2-assessment showed significantly fewer G-type carcinomas (P < 0.05). Each phenotype marker was less expressed in the submucosal part than in the mucosal part. In conclusion, CDX2 was a sensitive marker for assessing intestinal phenotype. A large portion of the early differentiated-type adenocarcinomas expressed CDX2 from the very early stage of carcinogenesis, and the proportion of G-type was unexpectedly low. Lower expression of each phenotype marker was considered the cause of phenotype alteration during submucosal invasion.