A correlation between the abilities of tumor cells to produce GM-CSF and form metastasis

Nearly a half of murine transplantable tumor cells upon in vitro culture were found to produce granulocyte/macrophage-colony stimulating factor-(GM-CSF) in the cultured fluids and express its mRNA in the cell. Tumor cells producing GM-CSF and expressing its mRNA in culture, when inoculated intramuscularly in the syngenic mice, developed severe metastasis with large tumor nodules in the lung and lymph nodes, whereas those producing no GM-CSF developed no visible metastatic nodules. With a possible mechanism involved in this intimate correlation between the production of GM-CSF and tumor metastasis, a role of GM-CSF as an autocrine growth factor in tumor growth and an immunopathological effect of GM-CSF on microenvironment of tumor cells in the metastatic tissues were discussed.