Detection of Epstein-Barr virus genome within thymic epithelial tumours in Taiwanese patients by nested PCR, PCR in situ hybridization, and RNA in situ hybridization

Epstein-Barr virus (EBV) is known to be associated with a variety of tumours, including Burkitt's lymphoma, nasopharyngeal carcinoma, and some carcinomas of other organs with similar lymphoepithelioma-like features. The association between EBV and thymic epithelial tumours is inconclusive, as reports in this regard are not entirely consistent and the methods employed are of different sensitivity and specificity. This study examined 78 thymomas and 21 thymic carcinomas in Taiwanese patients, to detect the viral genome at both DNA and RNA levels. The tissue blocks were first screened by nested polymerase chain reaction (PCR) targeting on the first tandem internal repeats. The positive cases were further submitted for viral localization by in situ PCR in situ hybridization (ISH) and Epstein-Barr-encoded RNA-1 (EBER-1) ISH. None of the thymomas showed a detectable EBV genome. Eight thymic carcinomas were positive for EBV by nested PCR, of which six displayed signals within the tumour cells by in situ PCR ISH and/or RNA ISH, one displayed signals within the lymphocytes, and one showed no discernible in situ signals. Most of them exhibited a lymphoepithelioma-like morphology. These results show that nested PCR is a sensitive method for screening the EBV genome in thymic epithelial tumours. In situ PCR ISH is reliable for localization of the virus, in addition to EBER-1 RNA ISH. Thymomas are not related to EBV, even in this endemic area. Thymic carcinomas, especially the lymphoepithelioma-like thymic carcinomas, are more often associated with the virus.