Research originally conducted in 2006 led to a suggestion that the development of prostate cancer in man might be associated with human infection by a gamma-retrovirus known as the xenotropic murine leukemia virus-related virus (XMRV). Later studies in 2009 also suggested an association between infection with XMRV and the onset of chronic fatigue syndrome (CFS).
Despite laboratory tests that supported this clinical association, there were also early signals that the proposed association was actually a consequence of contamination of laboratory specimens in mice that were involved in the original studies, and several later, independent studies were unable to show any link between prostate cancer or CFS and infection with XMRV.
A new paper by Lee et al. in PLoS One now appears to have finally confirmed that XMRV really was a contaminant that occurred accidentally during the processing of a specific set of prostate cancer cells in mice, leading to development of laboratory-derived cell lines that were infected with an abnormal strain of XMRV.
Lee et al. studied biological materials from two sources:
- A completely new set of prostate cancer tissues and plasma collected from a set of 39 patients
- Archival RNA and prostate tissues collected at the time of the original 2006 study
The authors were able to show, after application of extensive and sophisticated testing techniques, that:
- The archival ribonucleic acid (RNA) from the 2006 study still tested positive for XMRV, but …
- There was no sign of XMRV in any of the newly collected prostate cancer tissues or plasma.
- There was no sign of XMRV in any of the archival prostate tissues used for the original 2006 study.
- Specifically, there was no sign of XMRV in the archival VP62 prostate tissue from which the prototype XMRV strain of virus was derived.
- RNA sequences from viral genomes and human mitochondria showed that all previously characterized XMRV strains are identical and that the archival RNA had been contaminated by an XMRV-infected laboratory cell line.
These data certainly appear to confirm that, in fact, there really is no association between XMRV and prostate cancer, and that XMRV is not even a naturally acquired human infection.
It seems likely that — despite this and other data — the idea that prostate cancer may be an XMRV-induced type of cancer will remain alive and well on the Internet for years to come. In addition, we should be clear that there may still be some as yet unexplained relationship between a viral (or other) infection of the prostate and an increase in risk for prostate cancer either a few or possibly many years later. Just because prostate cancer does not, in fact, appear to be associated with this particular mouse virus also does not rule out the possibility that some other virus might be involved — but there is no clear indication of any such a relationship at the moment.