CSF1R (macrophage colony-stimulating factor 1 receptor) is a tyrosine kinase and receptor for CSF1 and IL34. Ligand binding to CSF1R activates PI3K-AKT-mTOR, RAS-RAF-MEK-ERK and STAT signaling pathways. Simple mutations in CSF1R are seen in about 1% of tumors, including 3% of colorectal cancers and 4% of skin cancers. Agents that target CSF1R are under clinical development as a treatment for cancer.