Phenotypical change of murine mammary tumors induced by treatment with GM-CSF. The tumors were removed after the final EPR measurement, sectioned, and stained for the presence of tumor macrophages (F4/80 antigen), blood vessels (von Willebrand factor antigen), or for the presence of HIF-1α. The PBS-treated tumors have less tumor macrophages, increased blood vessels, and less HIF-1α than those tumors treated with GM-CSF. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]