Some Observations on the Epidemiology and the Pathology of Reticulum Cell Sarcomas in (C57BL/Cne x C3H/Cne) F1 Mice

Abstract

Life-long observations on untreated animals have shown that spontaneous reticulum cell sarcomas (RCS) developed in 56.5 % male mice of the hybrid (C57BL/Cne x C3H/Cne) F1 strain; the average age at death of mice with tumors was 949 days, compared with 929 days for all causes: no age-specific peak of mortality has been shown to occur over the entire life span of the animals. Histologically, the spleen and all the lymphnodes, including the mesenteric node, were always invaded; neoplastic growth was found less frequently in kidneys, liver and lungs (77, 70, and 40%, respectively), only occasionally in other organs such as adrenals and testes, and never in the thymus. The tumor was predominantly composed of a single type of neoplastic cells, resembling highly undifferentiated reticular cells, typically proliferating from the periarteriolar region of the lymphatic follicles in the spleen. The monomorphic aspect of the tumor cell population suggests that RCS in this strain of mice may be classified as type A according to Dunn. Electron-microscopy observations showed the presence of a few virus-like particles both in tumor cells and in sediments from cell-free extracts. Transplantation of cells from spontaneous RCS into both normal and lethally-irradiated syngeneic recipients was successful only in 4 out of 7 experiments, regardless of the tissue of origin of the neoplastic cells (spleen, lymphnodes or bone marrow). Virus-like particles were seen with higher frequency in transplanted tumors. Inoculation of cell-free extracts into neonatal mice of low-leukemia strains has not so far been successful. Splenectomy of young animals as well as the intravenous injection of syngeneic bone marrow cells immediately following a lethal dose of whole-body X-irradiation significantly reduced the frequency of spontaneous tumors.