Evidence has emerged that the human polyoma virus BK might be associated with prostate cancer; this cancer is the second most important cause of cancer-related fatalities in men in the United States. BK DNA and proteins were found in prostate cancer cells at a certain stage of the development of the cancer (called atrophic lesions) which are an early stage in the development of the cancer. Current information does not show that BK virus causes prostate cancer but it indicates that virus proteins are present in cells that are on the way to becoming cancerous. In 21 samples of prostate adenocarcinoma, scientists looked for the presence of T antigen, a virally-encoded protein that is involved in stimulating the cell to divide. In 71% of the samples, BK virus DNA was found while 43% contained T-antigen protein. This protein was found, however, only in atrophic lesions which is a precursor of full prostate cancer. These cells also contained high levels of p53 protein but T-antigen and p53 were in the cytoplasm and not in the nucleus. P53 is a tumor suppressor protein that binds to certain sites in the DNA in the nucleus to turn off genes that cause cell replication. It also induces the apoptosis (cell death) of certain abnormal cells. Thus the interaction between T-antigen encoded by the BK virus and cellular p53 so that p53 remains in the cytoplasm might explain why the tumor suppressor activity of p53 is reduced in these cells.

This is rather similar to the situation in cervical cancer which we know to be caused by certain human papilloma viruses. In this case, papilloma virus proteins not only bind to p53 and stop it interacting with sites in the DNA of the cell, they lead to proteolysis of p53.