Search for Virus in Human Malignancies. 2. In vivo Studies.

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Abstract
Extensive investigations were carried out in carefully controlled studies in newborn white Swiss mice (ICR/Ha) and hamsters to recover viruses or virus-like oncogenic agents from human malignant tissues. Altogether, 84 preparations from clinical specimens were tested. The human specimens were from leukemias and solid tumors and were tested as crude, filtered or fluoro-carbon-treated extracts, as fluids from cell cultures of human malignant tissues, or as fluids from grivet monkey kidney cultures inoculated with clinical materials. There was a considerable incidence of spontaneous neoplasia, especially mammary carcinoma, among the mice but a very infrequent occurrence of malignancy in hamsters. Prevention of nursing among the mother mice did not increase the incidence of mammary carcinoma. Sex segregation of mice with retention of a virginal status appeared, in a small study, to diminish tumor incidence among females considerably below that of freely breeding animals. There was no statistically significant difference in tumor incidence among the experimental animals inoculated with specimens derived from human malignant tissues compared with the controls except for a few cases of leukemia which occurred in the experimental group and in a slightly more frequent occurrence of hepatoma and pulmonary adenocarcinoma among these animals. The need for adequate numbers of animals, for proper control procedures, and for extensive histologic examination of all abnormal animal tissues in studies of the role of transmissible agents in human malignancy was emphasized. The negative findings in these investigations were not interpreted as positive evidence for a non-viral etiology in malignancies of man.