INTRODUCTION

A substantial burden of human cancer worldwide is attributable to infection. Viral infections account for approximately 15 % of all human cancers. Cervical cancer, hepatocellular carcinoma and Kaposi's sarcoma, all caused by viruses, are some of the most important tumours in sub-Saharan Africa.

The interface between infection and malignancy is highlighted by the cancers prevalent in immunocompromised patients (Table 1). Human immunodeficiency virus (HIV)- infected individuals are specifically prone to cancer caused by viruses, e.g. Epstein–Barr virus (lymphomas), papillomaviruses (squamous carcinomas of skin and ano-genital carcinoma) and Kaposi's sarcoma-associated herpesvirus (lymphomas, multicentric Castleman's disease and Kaposi's sarcoma). The tumours increased in HIV-infected individuals where a virus has not yet been described (Table 1) may nevertheless have a viral aetiology. Carcinogenesis is a multifactorial process and not all persons infected with oncogenic viruses will develop a cancer: in fact, only a fraction of infected individuals will develop a tumour, particularly in the absence of immunosuppression. Certain tumours with a known viral aetiology (e.g. nasopharyngeal and hepatocellular carcinoma) are not increased in AIDS, indicating that viral infection and immunosuppression, without co-factors, are not enough to precipitate those specific cancers. Efficacious immunization against the primary infection would virtually eliminate the occurrence of the tumour with which the virus is associated. A successful vaccine against hepatitis B is available, whereas vaccines against Epstein–Barr virus and human papillomaviruses are currently in clinical studies.

This review will focus on the neoplasia associated with the gammaherpesviruses Epstein–Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV).