Although tumor-cell-derived GM-CSF markedly upregulated MCP-1 production by macrophages in vitro, neutralization of GM-CSF in tumor-bearing mice showed little effect on serum MCP-1 concentration or tumor MCP-1 content, strongly suggesting that the GM-CSF is not a major regulator of MCP-1 production in 4T1 tumor microenvironment. The gene discussed is CCL2; the disease is neoplasm.