In vivo tumor growth enhancement by granulocyte colony-stimulating factor

The intraperitoneal administration of human recombinant granulocyte colony-stimulating factor (G-CSF) enhanced the growth of intradermally inoculated tumor in mice; in a Meth A fibrosarcoma model, G-CSF administration significantly shortened the latency before tumor appearance, accelerated the increase of tumor size, shortened the survival time of tumor-bearing mice and increased the incidence of lethal tumor growth. A similar growth-enhancing effect of G-CSF was observed in models employing Meth 1 fibrosarcoma, colon carcinoma 26, and L1210 leukemia, although not all the effects were statistically significant. In vitro study showed that G-CSF did not enhance Meth A growth in suspension culture or in soft agar. These data suggest that G-CSF enhances the Meth A growth not directly but through the mediation of host factors. The accumulation of neutrophils was histologically observed in the tumor nodule, the blood, and the spleen in mice given G-CSF repeatedly. The spleen cells and the peripheral blood leukocytes of G-CSF-injected mice enhanced Meth A growth in vitro as compared with those of mice injected with physiological saline. These results suggest the possibility that the in vivo growth of tumor cells was enhanced by G-CSF-induced overproduction of cells including neutrophils.