ABSTRACT
Viruses are involved in cancers because they can either carry a copy of one of these genes or alter expression of the cell’s copy of one of them. Such viruses are called cancer-causing viruses, oncoviruses, or tumor viruses. Till the dawn of 19th century, viruses were classified as small infectious agents that, unlike cells and bacteria, pass through fine-pore filters. According to the World Health Organization cancer report 2008, some cancer-causing viruses are responsible for up to 20% of cancer deaths worldwide. Broadly, there are two different families of oncogenic viruses that depend on the type of nucleic acid present in the viral genome and the type of strategy to induce malignant transformation. Tumor viruses induce oncogenesis through manipulating an array of different cellular pathways. These viruses initiate a series of cellular events that lead to immortalization and proliferation of the infected cells by disrupting the mitotic checkpoint upon infection of the host cell.
