Xenotropic murine leukemia virus–related virus (XMRV) is a retrovirus which was first described in 2006 as an apparently novel human pathogen found in tissue samples from people with prostate cancer.

[1][2] Initial reports erroneously linked the virus to prostate cancer and later to chronic fatigue syndrome (CFS), leading to considerable interest in the scientific and patient communities, investigation of XMRV as a potential cause of multiple medical conditions, and public-health concerns about the safety of the donated blood supply.

[12] MLVs belong to the virus family Retroviridae and the genus gammaretrovirus and have a single-stranded RNA genome that replicates through a DNA intermediate.

[16][17] XMRV was discovered in the laboratories of Joseph DeRisi at the University of California, San Francisco, and Robert Silverman and Eric Klein of the Cleveland Clinic.

[24][25] Concerns arose as multiple subsequent studies failed to replicate the positive findings of XMRV in the blood of patients with CFS, prostate cancer, and other illnesses.

[31] Multiple contemporary studies concluded that XMRV was most likely a result of incidental recombination of mouse viruses during prostate cancer research in the 1990s.

[2][36][21] This included the initial study which had linked XMRV to CFS, which was retracted at Silverman's request; one of the co-authors, Judy Mikovits, was also accused of scientific misconduct.