Telomere repeat amplification protocol (TRAP) in situ reveals telomerase activity in three cell types in effusions: malignant cells, proliferative mesothelial cells, and lymphocytes.

Telomerase Repeat Amplification Protocol (TRAP) in situ was performed on cytospin preparations from 65 effusions from the serous cavities (45 pleural and 19 ascitic fluids and one pericardial fluid) submitted for routine diagnosis and the results were correlated to cytological morphology. Three types of cells with nuclear fluorescence were identified: malignant cells, hyperplastic mesothelial cell and lymphocytes. Of 38 cytologically malignant effusions, 12 showed strong reactivity in all malignant cells, three strong reactivity in part of the malignant population, whereas 12 showed moderate reactivity in the whole and five in part of the malignant population, respectively. In five malignant effusions weak reactivity was found in all (one case) and in scattered (four cases) malignant cells. Two effusions contained telomerase-negative malignant cells. Two pleural and two ascitic fluids contained proliferative mesothelial cells with weak or, in one case, moderate reactivity. Lymphocytes usually showed weak telomerase activity. Telomerase was expressed in almost all malignant tumours metastatic to serous cavities. Heterogeneity in tumour populations was demonstrated, which may have diagnostic implications, especially in cytology. Weak or moderate reactivity was found in lymphocytes and in some mesothelial proliferations and may explain the low specificity for malignancy sometimes obtained with the TRAP extract method. The weak reactivity found in lymphocytes may reduce the specificity when the extract method is used but causes no diagnostic problem with the TRAP in situ method.