KRAS and neoplasm: This effect activates macrophages into a TAM-like phenotype, forming a positive feedback loop.259 Pancreatic cancer cells can secrete CCL5 to promote the recruitment of Treg cells into the tumor site.262,263 The levels of tumor-derived GM-CSF,249 M-CSF,249 CSF1,264 CCL2, and CXCL5265,266 are often highly elevated by mutant KRAS expression and are associated with TAM infiltration.