Approximately 20% of all human cancer cases worldwide have been associated with infectious agents. This proportion is even higher in low-income countries, where, because of socioeconomic conditions, infections are more common and health-care surveillance is less available than in high-income countries. On the basis of a vast number of biological and epidemiological studies, the International Agency for Research on Cancer (IARC) has classified six viruses and one bacterium as human carcinogens: high-risk mucosal human papillomavirus (HPV) types, hepatitis C virus (HCV), hepatitis B virus (HBV), human T-cell lymphotropic virus type I (HTLV-1), Epstein–Barr virus (EBV), Kaposi sarcoma-associated herpesvirus (KSHV), and the bacterium Helicobacter pylori.
The estimate of 20% of cancer cases being associated with pathogens may in fact be rather low, and new evidence supports the involvement of additional infectious agents in human carcinogenesis. Over the past decade, it has become evident that the high-risk mucosal HPV types, already well known as oncogenic viruses responsible for cervical cancer, are also associated with a subset of oropharyngeal cancers. It is likely that other associations between established oncogenic viruses and various cancer types in humans remain to be discovered. A recently discovered human polyomavirus, Merkel cell polyomavirus (MCPyV), is associated with the rare tumour Merkel cell carcinoma. Early epidemiological studies suggest that infection with MCPyV is widespread in humans, and additional tumour associations may still be discovered. Ongoing studies of a subgroup of HPV types that infect the skin support their involvement, together with ultraviolet radiation (including sun exposure), in the development of squamous cell carcinoma in normal populations. It is likely that other viruses are able to cooperate with environmental risk factors, as observed for cutaneous HPV types and ultraviolet radiation.
This meeting, a joint initiative of IARC and the German Cancer Research Center (Deutsches Krebsforschungszentrum; DKFZ), will focus on discussion and critical evaluation of the epidemiology, immunology, and biology of cancer-associated viruses. The meeting programme emphasizes new HPV-related cancer types and newly discovered human polyomaviruses. Advances concerning other pathogens will also be incorporated as they arise.