Malignant pleural effusions due to small cell carcinoma of the lung. An immunocytochemical cell-surface analysis of lymphocytes and tumor cells.

Thirteen malignant pleural effusions due to small cell carcinoma (SCC) of the lung were immunocytochemically studied using the peroxidase-antiperoxidase adhesive slide assay for the determination of cell surface antigens. A panel of monoclonal antibodies (MAbs) was used to determine the lymphocyte subpopulations and the reactivity of the tumor cells. Of the lymphocytes, 87 +/- 1% were CD3+ T cells, with 72 +/- 10% CD4+ helper/inducer T cells and 20 +/- 5% CD8+ suppressor/cytotoxic T cells. Only a minority of T lymphocytes were activated in terms of expressing the surface markers CD38 and HLA-DR. The distribution of the lymphocyte subpopulations was not significantly different from the distribution in other malignant and nonmalignant pleural diseases previously studied, indicating that the reaction pattern of the lymphocytes in the pleural cavity is similar in different diseases. The tumor cells from all cases were positive for LeuM1, CD16 and HLA-DR; 10 of 11 cases were positive for HEA-125, Sam 2 and Sam 10. Positivity for epithelial membrane antigen was observed in 11 cases, for OKT9 in 8 cases and for carcinoembryonic antigen in 6 cases. A total or partial loss of the reactivity with HLA-1 was found in nine cases. The reactivity pattern of the tumor cells with the MAbs used in this study is not specific for SCC of the lung because other carcinoma cells also reacted with these markers. Additional morphologic criteria, such as cell size and cell configuration, are needed to recognize the immunocytochemically positive-reacting cells as tumor cells from SCC of the lung. However, the immunostaining allows a better identification of the tumor cells, especially in cases with a small quantity of tumor cells.