Cytokeratin polypeptide in gastrointestinal adenocarcinomas displaying squamous differentiation. 
In the present study we investigated the cytokeratin (CK) polypeptide expression in gastric and colonic adenocarcinomas.  A battery of monoclonal anti-cytokeratin-specific antibodies and anti-vimentin were used.  While the majority of cases displayed simple epithelial characteristics, in three of 17 cases of gastric adenocarcinomas and in one of 20 cases of colonic adenocarcinomas, CK polypeptides 13 (54 kd) and 16 (48 kd) were occasionally detected.  These CK polypeptides, characteristic of squamous nonkeratinizing epithelia, were found in cases in which no evidence of squamous differentiation could be demonstrated by histologic examination.  We believe that the presence of these unique CK polypeptides points to the squamous differentiation potential of the tumor cells.