Macrophages supply cancer cells with chemical growth factors and help build the new blood vessels required by a growing tumor. So intimately are they involved with the deadly progress of cancer that they can account for up to 50 percent of a tumor’s mass. Macrophages also appear to be necessary if the cancer is to progress to its deadliest phase, metastasis, and if a cancerous mouse is treated to eliminate all its macrophages, the tumor stops metastasizing.
