The frequency of infection by agents such as EBV, HBV or HTLV-1 are far greater than the incidence of the cancers with which they are linked. Viruses may act in concert with other factors in the evolution of cancer. The other factors might be genetic, immunological or environmental. Cell transformation by viruses is accompanied by the persistence of all or a part of the viral genome. It is also accompanied by the continual expression of a limited number of viral genes.
Viral oncogenes disrupt the normal cellular gene expression and signal transduction pathways.
The signal transduction pathway is responsible for altering cellular gene expression in response to a wide range of external and internal signals. Viral oncogenes disrupt the normal functioning of this net. They do this by virtue of altered structures or overproduction. The end result is an altered transcriptional profile which favours cell division. Transmembrane signalling apparatus including the cytoplasmic domain of receptors and submembranous components that are functionally linked to surface receptors.