The results of our in vitro study suggested that GM-CSF secreted by tumor cells regulate the production of MCP-1 in 4T1 tumors; therefore, neutralization of GM-CSF in tumor-bearing mice may reduce MCP-1 production in 4T1 tumor microenvironment and subsequent lung metastasis of 4T1 cells. The gene discussed is CSF2; the disease is neoplasm.