A special case in contemporary etiological studies is definition of the role of viruses in the pathogenesis of human
cancer. Virus–associated cancer develops only in a small minority of infected subjects, which implies that, if the
virus does play a role in the pathogenesis of the malignancy, other factors must be also involved. The author
summarises the general properties of human tumour viruses, reviews the development of causal thinking in
microbiology and proposes guidelines that might help to determine the role of viruses in human cancer.
role of viruses, malignant tumors.