Absence of SV-40 large T antigen (Tag) in malignant mesothelioma effusions: An immunocytochemical study

Simian Virus 40 (SV 40) was recently implicated in the pathogenesis of mali gnant mesothelioma. The oncogenic capacity of SV-40 is a function of a nucl ear protein, the large T antigen (Tag). SV-40 Tag DNA sequences are detecte d by the polymerase chain reaction in 40-80% of malignant mesothelial proli ferations. However, the role of immunohistochemistry (IHC) in demonstrating the nuclear localization of Tag is controversial. We sought to determine t he clinical utility of SV-40 Tag IHC in pleural effusion cytology as an anc illary tool in the cytologic diagnosis of malignant mesothelioma (MM). Form alin-fixed, paraffin-embedded cell block sections from 100 pleural effusion s (32 MMs, 25 benign reactive, 43 metastatic adenocarcinomas) were immunost ained for the SV-40 anti-Tag, using two primary monoclonal SV-40 Tag antibo dies: clone Pab 416 and clone Pab 101. Despite strong and consistent immuno reactivity in positive controls, no nuclear immunostaining was observed in an), case. We believe the small sample size in cytology cell block sections , the low viral copy number in infected cells, and the effect of formalin f ixation may have resulted in absence of immunoreactivity. The role of SV-40 Tag IHC in diagnostic cytopathology remains unclear unless further studies reliably show its detection.(C) 2001 Wiley-Liss,Inc.