STAT5 is activated in macrophages by breast cancer cell-derived factors and regulates macrophage function in the tumor microenvironment.

Breast cancer cells produce soluble factors, such as GM-CSF, that activate the STAT5 pathway in macrophages and drive expression of inflammatory factors. STAT5 deletion in myeloid cells enhances metastasis, suggesting that STAT5 activation in tumor-associated macrophages protects against tumor progression. Understanding mechanisms that drive macrophage function in the tumor microenvironment will ultimately lead to new approaches that suppress tumor-promoting functions while enhancing their anti-tumor functions.