M-CSF (CSF-1) is the primary regulator of macrophage survival, proliferation and differentiation. It is essential for macrophage-related functions such as bone resorption, vascular development, and innate immunity. It signals through M-CSF R on monocytes, tissue macrophages, and osteoblasts. Both M-CSF and its receptor can be expressed by tumor cells, allowing M-CSF to act as an autocrine growth factor for cancer cells. Full length M-CSF is expressed as a transmembrane dimer, but various additional forms can be generated by alternative splicing, differential glycosylation, chondroitin sulfate proteoglycan modification, and proteolytic shedding.