Prospects for reducing virus-associated human cancers by antiviral vaccines.

The last 25 years have seen a major effort to identify human viruses that either cause cancer in humans directly or can be considered significant cofactors or promoters of cancer. The prevailing view is that tumor-associated viruses are necessary but not sufficient for tumor causation. A long latent period between the initial infection and the appearance of the neoplasm is the norm. Generally, the virus implicated as causative is integrated into cellular DNA. Various virus types have been identified; these include both DNA- and RNA-containing agents from the hepadnavirus, herpesvirus, papovavirus, oncornavirus, and lentivirus groups. Although these candidate viral agents are less prevalent in the developed world, hundreds of millions of people are infected world-wide, and about 1 million infected people develop virus-associated tumors annually. Furthermore, nonviral cofactors are suspect or have been identified in the genesis of many virus-associated cancers. A major global approach to prevention of the initial infection can be made by developing efficacious and cost-effective vaccines. An approved human vaccine is available in one case, whereas in every other situation indications exist that a candidate vaccine may soon be available.