There are three potential mechanisms by which MCP-1 production is increased in tumors: (1) tumor cells constitutively produce a high level of MCP-1, (2) tumor cells produce a high level of MCP-1 in response to stimuli, and (3) stromal cells produce a high level of MCP-1 in response to stimuli, such as a tumor cell product(s). This evidence concerns the gene CCL2 and neoplasm.