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Occurrence and expression of cytokeratins in carcinoid tumours of the gastrointestinal tract and their probable precursor cells.

Occurrence and expression of cytokeratins were studied by the immunoperoxidase-antiperoxidase (PAP) technique in formalin-fixed, paraffin embedded material from 18 cases of carcinoid tumours of the gastrointestinal tract. Polyclonal antikeratin for wide spectrum screening was detected in 12 cases; low molecular weight cytokeratins, C19 and CAM5.2 were positive in majority of the cases whereas antikeratins for high molecular weight were negative in all. Similar positive immuno-reactivity with antibodies to cytokeratins were detected in the surrounding epithelial cells. These results suggest that carcinoids of the gastrointestinal tract originate from the endodermal stem cell and differentiates along one or more directions, and the immunohistochemical findings depend upon the direction of their differentiation.