XMRV - A New Prostate cancer virus?

In 2006 some US researchers (see http://www.plospathogens.org/article/info%3Adoi%2F10.1371%2Fjournal.ppat.0020025) have unearthed evidence of a possible viral link to prostate cancer, yes prostate cancer! For years the primary belief that prostate cancer was exclusively caused by a number of factors including genetic, dietic and environmental has seemingly been dealt a strong blow. The aetiological (causative) complexity of cancer in its many forms suggest multifactorial causes however most of the scientific community has been slow and reluctant to accept microbial or infectious causes for cancers. The recent work involving HPV, the virus causing cervical cancer, has seemingly softened this stance. Nonetheless the caution exhibited is necessary since sound science is always founded on strict and unwaivering proof that is both reproducible and logical.

This leads to the most recent candidate for an infectious agent of prostate cancer, XMRV. The authors presented the first documented evidence of XMRV, a xenotrophic retrovirus in subset of human prostatic samples. Furthermore they proved that the virus XMRV was capable of replicating in human cells and this replication is regulated by interferon (IFN) and its downstream effector gene RNase L. The role of RNase L a gene coding for a unique ribonuclease that is essential in the production of interferon and XMRV was later investigated by this group of scientists.
This investigation showed a difference in the variation of this gene and the incidence of XMRV infection, where homozygous (QQ) recessive forms of the gene had higher incidence (40%) of infection than heterozygous (RQ) or homozygous dominant (RR) forms (1.5%) of the gene.

Notwithstanding some skepticism and reservation for full acceptance of this virus as a cause of prostate cancer still exists. Studies from researchers in Germany have failed to reproduce the levels of incidence of XMRV infection in prostate samples or even establish the presence of XMRV in German patients. From previous studies the genetic make-up (Rnase L gene) of the cohort appears to influence XMRV incidence. Another group of US researchers did find XMRV infection in prostate cancer patients albeit at a lower incidence than that originally found (40% vs 6%). They found "...XMRV infection to be independent of a common polymorphism in the RNASEL gene, unlike results previously reported"." In addition they found that the association was greater with higher grade tumours. (http://www.pnas.org/content/106/38/16351.abstract)


There are a number of questions which remain unanswered. These include how does a man become infected with XMRV? What is the reservoir or source of this virus? How can a man protect himself from becoming infected? What is the mode of transmission (sexual, respiratory, blood borne etc)? Future studies involving patients in different geographic areas to investigate the prevalence of XMRV not only in prostate cancer patients but also in healthy individuals both male and female and possible animal reservoirs could offer more insight into the mode of transmission.

This possible candidate for prostate cancer underscores the dynamic nature of the knowledge of the interaction between man and viruses in the environment.