Introduction to virus-caused cancer: Type C virus

Abstract

Ribonucleic acid-containing, C-type viruses have been isolated from almost every class of animals; they transform cells in vitro and cause leukemias and sarcomas in vivo. Although these viruses are structurally, biochemically, and biologically similar, they can be distinguished from each other by individually characteristic nucleic acids and antigens. They are usually transmitted vertically; evidence of their presence, in the form of nucleic acid sequences homologous to viral nucleic acid sequences, may be detected in normal cells. Many C-type viruses are defective; helper viruses are needed for full viral genome expression. Human C-type leukemia or sarcoma viruses have not been identified with certainty yet, although their existence can be predicted from the results of experimental animal studies and immunologic, ultrastructural, and biochemical analyses of human tumors.