PCR can be used for the identification of a virus in a specimen. However, a positive PCR can be seen from the presence of a given virus either in the tumor cells or in the infiltrating reactive cells in a latently infected individual. Thus, a positive PCR result does not necessarily indicate that the tumor cells contain a specific virus. This problem is more common for EBV than for KSHV, since latent EBV infection is ubiquitous, while latent KSHV infection is not.29 Assays that are quantitative or semiquantitative can distinguish virus in tumor cells from infiltrating cells, where the viral copy number would be at least as high as the number of tumor cells. Infiltrating benign lymphocytes would correspond to a very small proportion of the total cell population unless active viral infection is present (such as infectious mononucleosis). Alternatively, for EBV, ISH for EBER can be used to confirm the presence of EBV in the tumor cells. For KSHV, the best approach for confirmation of a positive PCR result is immunohisto-chemistry with monoclonal antibodies for ORF73, which encodes the latency-associated nuclear antigen (LANA or LNA).
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