CSF1R is a transmembrane class III receptor tyrosine kinase cell surface protein belonging to the CSF1/PDGF receptor family. It is a receptor for CSF1 and IL34, and it controls the production, differentiation, and function of macrophages. It is an important inflammatory response mediator and is able to regulate release of proinflammatory cytokines from macrophages. CSF1R is overexpressed on tumor-associated macrophages and in many cancers. A class of drugs known as kinase inhibitors, or CSF1R inhibitors, bind to CSF1R. There are several CSF1R inhibitors currently approved for treatment of an array of cancers.