Macrophages had been known since the nineteenth century to gather at tumor sites, leading Virchow and others to speculate that cancer is caused by inflammation, meaning a gathering of leucocytes at some site of injury or infection. Or, more optimistically, one might imagine that the macrophages were massing for an assault on the tumor. Instead, it turned out that they spent their time in the neighborhood of tumors encouraging the cancer cells to continue on their reproductive rampage. They are cheerleaders on the side of death. Frances Balkwill, one of the cell biologists who contributed to
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