1 Origins of Contemporary DNA Tumor Virus Research

Abstract

THE CANCER CELL DEFINED
The evolution of unicellular organisms into multicellular organisms has demanded the emergence of very precise rules to govern both the spatial siting and the multiplication rates of their respective differentiated cells. A given specialized cell does not grow at any site in its multicellular host, but is restricted to have only certain cell types for its neighbors and to proliferate only upon receipt of a message signifying that more of its kind are needed for the orderly growth or maintenance of the complete organism. Given the existence of so many types of multicellular organisms, each with its unique patterns of differentiation, there are likely to exist many, many molecular pathways along which these signals are transmitted. Any of them in turn may fail and lead to one of the many abnormal forms of growth that collectively are called cancer.

Cancer is therefore not a unitary category, but a wide (to some, hopelessly wide) collection of different abnormal conditions, each displaying its own specific properties. In thinking about how to study cancer, most investigators quickly see the need to distinguish the property of excessive cell division from the property of abnormal cellular affinities. The quality of uncontrolled growth is what leads to the localized masses of single cell types often referred to as tumors. When these tumors grow only at the sites of origin, they do not necessarily upset the functioning of their host and frequently are called benign tumors. However, when a cell that has lost...