The heterogeneity of pancreatic cancer CAFs is further supported by recent research that identified a subpopulation of stromal cells that was designated as cancer associated mesenchymal stem cells that caused cancer cell invasion through granulocyte–macrophage colony-stimulating factor (GM-CSF) in one study and increased tumor cellular proliferation and larger tumors in a second study [5,52,53]. Here, CSF2 is linked to cancer.