Induction of Tumors in Adult Hamsters With Simian Virus 40

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Abstract
Certain effects of age and route of inoculation on simian virus 40 (SV40) tumor formation in Syrian hamsters have been examined. Approximately 20% of hamsters 4 months of age inoculated subcutaneously with virus developed tumors at the sites of inoculation after very long latent periods. Some tumors were transplantable and contained SV40 complement-fixing and transplantation antigens. In 4-month-old hamsters inoculated with virus directly into the cheek pouch, and in irradiated animals of this age inoculated subcutaneously, tumors appeared much sooner and in somewhat higher frequency than in intact animals inoculated subcutaneously. It is concluded that the resistance of adult animals to virus oncogenesis is relative, not absolute, and that potentially malignant cells can remain dormant for the greater part of the lifespan of the animals. Procedures that diminish the effectiveness of the host's immune response favor emergence of tumor cells.