In the present work the effect of a colony stimulating factor (CSFs), i.e. recombinant human granulocyte-macrophage colony stimulating factor (rhGMCSF), on tumor cell proliferation of a human renal cell carcinoma (RCC) and a squamous cell carcinoma (SCC) xenotransplanted into nude mice was studied. The measurement of the H-3-thymidine labeling index and the mitotic index of the tumor cells of both tumor lines as a function of the GM-CSF dose (0.05-1.00 mu g/g body weight) showed that the cell proliferation in both tumor types increases at low doses (p<0.05). Furthermore, the course of the dose dependent stimulation of cell proliferation is somewhat different for each tumor line. This possible growth stimulating effect of the rhGM-CSF found in the present work for both xenotransplanted tumor types should be considered, when this substance is applied within therapeutic regimens. Intertumoral differences should also be regarded.

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