Cytology: screening or diagnostic tool?

Previously used only as a screening tool, cytology now emerges as a powerful diagnostic technique, especially since the advent of the fine needle aspiration (FNA) biopsy. This article highlights the use of ancillary techniques, primarily electron microscopy (EM), and immunohistochemistry (IHC). When coupled with routine cytological examination such as FNA and body cavity fluid cytology, EM and IHC can refine the diagnosis and make it more precise. The authors discuss how to solve common diagnostic dilemmas by the use of cytology along with IHC and EM. The following common diagnostic problems are addressed: mesothelioma versus adenocarcinoma, neuroendocrine neoplasms and their mimickers, melanoma versus carcinoma versus sarcoma, hepatocellular carcinoma versus adenocarcinoma and adenocarcinomas of unknown primary.