A quantitative ultrastructural study of the pleomorphic adenoma (mixed tumor) of human minor salivary glands

A quantitative ultrastructural comparison has been made of the cells of seven pleomorphic adenomas and of five normal minor salivary glands. Criteria were adopted for the recognition of different cell types and calibration between observers was carried out. The relative volumes of cells in both normal and tumor material were obtained by the stereologic method of point counting. In normal glands, duct cells occupied 2.6%, myoepithelial cells 6.2%, acinar cells 77.8%, and other tissue elements 13.4% of tissue volume. By contrast, in the pleomorphic adenomas, duct cells occupied 61.5%, myoepithelial cells 4.9%, acinar cells 4.4%, and other tissue elements 29.2%. The differences between percentage volumes of cell types in tumor and normal gland were highly significant (p < 0.001). The higher proportion by volume of cells of duct origin in the pleomorphic adenomas than in normal glands indicates that these cells, rather than myoepithelial cells, are the major cells of the tumor in these glands.