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Approximately 15% of all human cancers worldwide have been associated with infectious agents (Plummer et al., 2016). This proportion is even higher in low-resource countries, where due to socioeconomic conditions, infections are more common and health care surveillance is less available than in high-resource 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-lymphotropic virus type 1 (HTLV-1), Epstein–Barr virus (EBV), Kaposi sarcoma–associated herpesvirus (KSHV), and the bacterium Helicobacter pylori.

The 20% estimate of pathogen-associated cancers 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 cancers, are also associated with a subset of oropharyngeal cancers. It is also likely that other associations between established oncogenic viruses and various human cancers 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 yet be discovered. Ongoing studies of a subgroup of HPV types that infect the skin suggest their involvement, together with ultraviolet radiation (including sun exposure), in the development of non-melanoma skin cancer (NMSC) in normal populations.

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 emerging HPV-related cancers and newly discovered human polyomaviruses. Issues concerning other pathogens will also be discussed as they arise.