The current role of electron microscopy in the diagnosis of epithelial and epithelioid tumors.

Electron microscopy may be applied to the study of epithelial or epithelial-like tumors with benefits similar to those encountered when it is applied to other diseases. Thus, it may complement and allow us to understand the light microscopic appearance of tumors, help in tailoring or reducing the number of antibodies, or lead to diagnosis in cases with paradoxical or nonspecific immunocytochemical results. An important, newly suggested application is to use it as a quality assurance tool in the evaluation of cases already diagnosed by other methods. Tumors with epithelial phenotype are highly prevalent, and therefore the number of problem cases can also be relatively high. In this article, we review the main ultrastructural features used in the differential diagnosis of epithelial and epithelioid tumors and some potential pitfalls. In addition, we summarize the criteria for differential diagnosis in specific topographical areas and analyze some examples of how electron microscopy may improve the accuracy of pathological diagnosis by interacting with currently available immunocytochemical panels.