Granulocyte-macrophage colony-stimulating factor inhibits tumor growth during the postoperative period

Background. Granulocyte-macrophage colony-stimulating factor (GM-CSF) may have important antineoplastic properties because it induces macrophage tumoricidal activity in vitro. We examined the inhibitory effect of GM-CSF on tumor growth in a murine carcinoma model and whether this inhibitory effect would persist during the postoperative period. Potential macrophage-mediated mechanisms were studied. Methods. The effect of GM-CSF on macrophage function in vitro was assessed by measuring superoxide anion and interleukin-6 production, percentage phagocytosis of Candida albicans, and percentage Ia expression. GM-CSF's effect on tumor volume was assessed first in a murine tumor model and second to examine whether these effects also occurred during the postoperative period in the same model after laparotomy. Macrophage function in the latter study was assessed by measuring superoxide anion, cytotoxicity, and tumor necrosis factor production. Results. GM-CSF treatment was associated with a decrease in tumor volume on day 4 after the initiation of GM-CSF treatment (0. 93 ± 0.08 cm³ for control versus 0.34 ± 0.08 cm³ for GM-CSF; p < 0.05). This effect was also seen after laparotomy (1.07 ± 0.2 cm³ for laparotomy + saline versus 0.16 ± 0.04 cm³ for laparotomy + GM-CSF, p < 0.05). In vivo macrophage function showed increased superoxide anion, cytotoxicity, and tumor necrosis factor-α production from macrophages obtained from GM-CSF treated animals compared with saline treated controls. Conclusions. Tumor growth is inhibited by GM-CSF treatment, and this effect also occurs after laparotomy. Thus GM-CSF may have a therapeutic role in the treatment of the tumor bearing hast after operation.