Human Tumor Viruses

Viruses are among the oldest known and most prevalent oncogenic agents. The quality of the evidence for the in vivo tumorigenic potential of microorganisms varies, thus accordingly, viruses were classified in 4 evidence-based categories by the International Agency for Research on Cancer in 2009. Since then, our understanding of the role of viruses in cancer has significantly improved, firstly due to the emergence of high throughput sequencing technologies that allowed the ¿brute-force¿ recovery of unknown viral genomes. Carcinogenesis is a multi-casual and multi-stage process and viruses, whether active or in latency, seem to act directly, indirectly, and synergistically with multiple co-factors towards the induction of cancer¿s hallmarks. To date, the worldwide burden of cancers with viral etiology accounts for almost 12% of cancer cases ¿ exceeding 20% in the developing world. According to the International Agency for Research on Cancer (IARC), seven viruses have been characterized as Group 1 carcinogens for humans but their part in cancer pathogenesis seems to vary among different viruses and different disease forms.