Viruses and tumor cell microenvironment: A brief summary

An infectious etiology for a number of cancers has been entertained for over 100 years and modern studies have confirmed that a number of viruses are linked to cancer induction. While a large number of viruses have been demonstrated in a number of types of cancers, most such findings have been dismissed in the past as opportunistic infections, especially with persistent viruses with high rates of infectivity of the world's populations. More recent studies have clearly shown that while not definitely causing these cancers, these viruses appear capable of affecting the biology of these tumors in such a way as to make them more aggressive and more resistant to conventional treatments. The term oncomodulatory viruses have been used to describe this phenomenon. A number of recent studies have shown a growing number of ways; these oncomodulatory viruses can alter the pathology of these tumors by affecting cell signaling, cell metabolism, apoptosis mechanisms, cell-cell communication, inflammation, antitumor immunity suppression, and angiogenesis. We are also learning that much of the behavior of tumors depends on cancer stem cells and stromal cells within the tumor microenvironment, which participate in extensive, dynamic crosstalk known to affect tumor behavior. Cancer stem cells have been found to be particularly susceptible to infection by human cytomegaloviruses. In a number of studies, it has been shown that while only a select number of cells are actually infected with the virus, numerous viral proteins are released into the cancer and stromal cells in the microenvironment and these viral proteins are known to affect tumor behavior and aggressiveness.