A drug used to treat HIV infection can slow the spread of prostate cancer.
Scientists hope the compound, or others like it, may help men live longer with the disease.
Early studies have demonstrated the antiretroviral drug maraviroc can dramatically curb the lethal spread of prostate cancer in mice.
The disease most commonly travels to the bones, leading to severe pain, disability and eventual death.
But treatment with maraviroc reduced the metastatis (spread) of prostate tumours to the bones, brain and other organs by 60pc in mice.
"This work shows we can dramatically reduce metastasis in pre-clinical models," said Dr Richard Pestell, of Jefferson University in Philadelphia.
"Because the drug is already approved for HIV treatment, we may be able to test soon whether it can block metastasis in patients with prostate cancer."
The drug targets a protein molecule on the surface of cells called the CCR5 receptor which the Aids virus HIV uses to invade white blood cells.
Previous research in 2012 showed CCR5 was implicated in the spread of aggressive forms of breast cancer to the lungs.
To investigate further, the scientists used maraviroc to block CCR5 in mice with metastatic prostate cancer. They found that compared with sick mice not given the drug, overall cancer spread was cut by 60pc.