A new human retrovirus associated with prostate cancer

Viruses and cancer have had a long history, beginning from the first discoveries of cancer viruses in animals in the late 19th century. Animal cancer viruses have provided great insights into fundamental processes of cancer, such as the discovery of cellular protooncogenes and tumor suppressor proteins (1). More recently, the involvement of viruses in human cancer has been established (2). It is now estimated that 20–25% of human cancers worldwide have a known viral etiology (2) (Table 1), although, given the multifactorial nature of carcinogenesis, other factors also contribute. In some cases, the viruses directly promote tumor development through expression of viral protein(s) that alter the growth properties of the tumor cell. For instance, the E6 and E7 proteins of oncogenic human papillomaviruses (HPVs) bind and inactivate cellular tumor suppressor proteins (3). In other cases viruses may indirectly cause cancer; the tumor cells themselves may not express the virus. Hepatitis B and C viruses appear to cause liver cancer by inducing chronic destruction and compensatory replacement of hepatocytes; the continual hepatocyte division may establish a cellular environment where other changes lead to cancer. In addition, human immunodeficiency virus (HIV) that causes AIDS indirectly causes cancer by crippling immune defenses against cancers induced by Kaposi's sarcoma herpes virus/HHV-8, Epstein–Barr virus, and HPV 6. Viral involvements in human cancer have practical implications. First, prevention of infection may reduce the risk of developing cancer; vaccines for oncogenic HPV have recently been approved for prevention of cervical cancer. Second, mechanistic studies may identify viral or cellular targets for cancer treatment or prevention. In this issue of PNAS, Dong et al. (4) provide evidence for a new human retrovirus associated with familial prostate cancer (PC).

Studies of rare families with predispositions to cancer have led to identification of tumor suppressor …

*E-mail: hyfan{at}uci.edu