Epstein-Barr virus: the first human tumor virus and its role in cancer.

The Epstein-Barr virus (EBV) is classically associated with three malignancies, Burkitt's lymphoma. B-cell lymphoproliferative syndromes, and nasopharyngeal carcinoma, and, more recently, with Hodgkin's disease, T-cell lymphomas, and gastric carcinoma, as well as being the causal agent for infectious mononucleosis. The relation of the virus to the malignancies varies from primary etiologic agent to necessary or contributory cofactor. Clonal EBV episomes are found in all the malignant conditions. EBV infects both epithelial and lymphoid cells, providing a pathobiological basis for these diverse associations. Most of the malignancies occur after years of viral dormancy and are accompanied or triggered by viral reactivation, in contrast to infectious mononucleosis, which results from primary infection with EBV. The EBV-associated malignancies offer insights into the causation and early detection of cancer. The molecular virology and pathobiology of EBV infection states provide the basis for the specific diagnosis of these diseases and a framework for new therapies.