Detection of latent Epstein-Barr virus (EBV) DNA in paraffin sections of nasopharyngeal carcinomas expressing no EBV-encoded small RNAs using in situ PCR.

In situ hybridization (ISH) with EBER 1 (Epstein-Barrvirus (EBV)-encoded small RNA1) probes is widely used for in situ detection of EBV-infected cells. ISH with an EBER1 probe showed that 10 of 40 NPC cases were negative for EBER1 expression. For in situ detection of EBV DNA, we used in situ PCR method which can detect one copy of EBV DNA per cell. Of the 10 EBER1-negative cases, three cases including one each of well- and poorly differentiated carcinomas and undifferentiated carcinoma were EBV DNA-positive by in situ PCR. The remaining seven were truly negative for the presence of EBV DNA. All the EBV genome-negative NPC cases examined here were histologically classified as poorly differentiated or undifferentiated carcinomas which are known to be closely associated with EBV, indicating the existence of EBV DNA-negative NPC cases, regardless of histological type or differentiation. These results indicate that there are EBV genome-positive NPC cases expressing no EBER1 and that in situ PCR can be suitable for in situ detection of EBV-infected cells, especially those expressing no EBER1 in paraffin sections.