The Complex Etiology of Cancer.

The recognized causes of cancer are briefly reviewed, and the inadequacy of present knowledge to explain cancer incidence and distribution is pointed out. New knowledge and concepts concerning carcinogenesis are then discussed, emphasizing the combined effect of mutiple factors; recent advances in the knowledge of the nature, growth, and pathogenicity of viruses; and the role of host factors. The concept of a complex etiology —the concurrent or sequential action of multiple etiologic factors (co-carcinogenesis in its broadest definition)—is suggested as a plausible explanation for the incidence pat terns of clinical cancer.