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Immunohistochemical detection of cytotoxic lymphocytes in malignant serous effusions

The use of ancillary techniques to aid in the diagnosis of metastatic carcinoma in serous effusions has been the subject of numerous studies. In this article, we study 35 cases of malignant effusions (metastatic adenocarcinoma) and 20 benign effusions using a panel of immunohistochemical markers to determine whether changes in the subpopulations of accompanying lymphoid cells can be detected with this technique and whether such changes are associated with the presence of malignancy. We noted a significant increase in cytotoxic lymphocytes, defined as the percentage of all lymphoid cells staining with an antibody to TIA‐1 (an antigen localized to the cytotoxic granule membranes of cytotoxic T cells and natural killer cells) in malignant compared with benign effusions (23% vs. 12%; P < 0.05). In addition, nearly all cases in which cytotoxic lymphocytes composed >20% of the lymphoid cell population contained metastatic tumor. Thus, immunohistochemical staining for TIA‐1 can reliably detect cytotoxic lymphocytes in cell blocks of serous effusions; in addition, a relative increase in their number is associated with the presence of malignancy. Diagn. Cytopathol. 1999;21:18–21. © 1999 Wiley‐Liss, Inc.