Two of the most important needs for a more adequate animal-testing program to keep pace with the avalanching stockpile of candidate chemical compounds in the field of cancer chemotherapy are: (1) a new order of magnitude in the production of biologically uniform indicator tumors which simulate naturally occurring spontaneous tumors of laboratory animals, and (2) greater sensitivity and precision of the indicator reactions used for detecting antitumor effects. The first of these objectives can already be achieved with several of the established viral tumors of laboratory animals. There is also some preliminary evidence that, under properly controlled test conditions, the viral tumors may provide a basis for significant advances toward the second objective, that is, for increasing both the sensitivity and the precision of antitumor indicator responses.

In a discussion of this same general subject about 2 years ago, Endicott pointed out that serious efforts had not been made toward the use of viral tumors for screening or therapeutic testing, though pilot experiments involving the Rous sarcoma and Friend viruses were then under way. The chief reason given for the delay in use of viral tumors was the lack of sufficient knowledge concerning their biology ". . . to permit the chemo-therapist to establish a reliable test system."

It will be among the purposes of this discussion to illustrate the types of biological information that are needed with respect to both the virus and the host, in order that the chemotherapist may be able to devise adequate test systems; also, a brief review will be given of results that have been obtained in therapeutic and prophylactic tests involving viral tumors, including advanced information on the pilot studies mentioned by Endicott. The advanced information that will be given was kindly supplied by Doctors Vincent Groupe and Kanematsu Suguira, for the Rous sarcoma and Friend viruses, respectively.