Congenital polycystic tumor of the atrioventricular node (endodermal heterotopia, mesothelioma): a histogenetic appraisal with evidence for its endodermal origin.

The small, variously designated, primary atrioventricular node tumor has been considered to be of endothelial, endodermal, or mesothelial origin. To identify its derivation, we studied seven tumors using silver staining and immunocytochemical labeling with a variety of antibodies. Cytoplasmic argyrophil granules but not argentaffin granules were found in isolated cells among the more numerous tubule-lining cells in four tumors. Serotonin and calcitonin were demonstrable in seven and six tumors, respectively, in a similar distribution to that of the argyrophil cells. A positive reaction of different distribution from that of the argyrophil cells was noted in a varying number of tubule-lining cells for carcinoembryonic antigen, epithelial membrane antigen, and blood group antigen in seven, four, and seven tumors, respectively. No activity was noted in the tumor cells for factor VIII-related antigen or a number of peptides. An endodermal rather than mesothelial or epithelial origin for the tumor is substantiated by the presence of neuroendocrine cells in the midst of the more numerous carcinoembryonic-antigen-positive lining cells of the tumor tubules.