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Physiological and pathological bone resorption is mediated by osteoclasts, multinucleated cells which are formed by the fusion of monocyte / macrophage precursors. The canonical pathway of osteoclast formation requires the presence of the receptor activator for NFkappaB ligand (RANKL) and macrophage colony stimulating factor (M-CSF). Non-canonical pathways of osteoclast formation have been described in which cytokines / growth factors can substitute for RANKL or M-CSF to induce osteoclast formation. Substitutes for RANKL include LIGHT, TNFalpha and interleukins 6, 11 and 8. M-CSF substitutes include vascular endothelial growth factor (VEGF), placental growth factor (PlGF), FLt-3 ligand and hepatocyte growth factor (HGF). These growth factors can also influence canonical (RANKL / M-CSF-induced) osteoclast formation. Both canonical and non-canonical pathways of osteoclast formation play a role in the formation of osteolytic lesions where there is increased osteoclast formation and activity, such as in giant cell tumour of bone.

Original publication




Journal article


Histol histopathol

Publication Date





337 - 346


Cytokines, Humans, Macrophage Colony-Stimulating Factor, Models, Biological, Osteoclasts, Osteolysis, RANK Ligand, Receptor Activator of Nuclear Factor-kappa B, Tumor Necrosis Factor-alpha