Interleukin-34 is expressed by giant cell tumours of bone and plays a key role in RANKL-induced osteoclastogenesis.

Interleukin-34 (IL-34) is a newly discovered regulator of myeloid lineage differentiation, proliferation, and survival, acting via the macrophage-colony stimulating factor receptor (M-CSF receptor, c-fms). M-CSF, the main ligand for c-fms, is required for osteoclastogenesis and has been already identified as a critical contributor of the pathogenesis of giant cell tumours of bone (GCTs), tumours rich in osteoclasts. According to the key role of M-CSF in osteoclastogenesis and GCTs, the expression of IL-34 in human GCTs was first assessed.