Morphology of the Oncogenic Response of Hamsters to Polyoma Virus Infection

Abstract

The distribution, morphology, and pathogenesis of tumors occurring in 274 hamsters subcutaneously inoculated with different dilutions of fluid from cultures of mouse embryo cells infected with polyoma virus are described. Inflammatory and specific degenerative changes preceded tumors in some sites, but not all sites. The kidney, heart, liver, and subcutaneous tissues were common sites of primary tumors, but other sites may be affected. Unique metastases from the earliest proliferative lesions occurred in the lung. Some tumors in the liver were simple cystic angiomas composed of endothelial cells; focal proliferation of renal tubules in a few animals was the only response of epithelium observed. The solid tumors in all sites had common structural characteristics suggesting origin from poorly differentiated mesenchyme possibly associated with components of the vascular wall. Tumors varied little in structure, but subcutaneous and cardiac tumors additionally contained fat cells, and cardiac and bone marrow tumors contained areas of atypical osteogenesis. The number of primary tumor foci in an organ was determined by the amount of tissue culture fluid inoculated. With large doses, confluent tumor foci developed that were rapidly lethal; with smaller doses, tumor foci with the same histologic characteristics developed but they were isolated, which allowed longer survival. The histology and apparent behavior of the tumors in the surviving animals indicated a few had all the qualities of highly malignant fibrosarcomas, while others lost even the simple ability to continue proliferation. Most tumors continued to grow, but formed ever-expanding, circumscribed nodules with limited ability to invade or destroy tissues. These nodules may be exceptionally valuable research tools, since their cells seemed to deviate from normal immature cells only in the ability to continue growth.