Modern Interpretation of Giant Cell Tumor of Bone: Predominantly Osteoclastogenic Stromal Tumor

Giant cell tumor (GCT) of bone has occupied a central stage in musculoskeletal tumor practice because of its relatively common incidence, striking features of giant cell formation, severe destruction of bone (osteolysis), diverse but controversial topical adjuvant therapeutic options, and preponderance for local recurrences.GCT has oft en been referred to as osteoclastoma due to its unusually high population of multi-nucleated giant cells.1,2) Th e terms GCT and osteoclastoma have given the impression of giant cells as being the major neoplastic component of the lesion.Many new pathophysiologic concepts have emerged since the discovery of a new paradigm of osteo-Owing to striking features of numerous multinucleated cells and bone destruction, giant cell tumor (GCT) of bone, often called as osteoclastoma, has drawn major attractions from orthopaedic surgeons, pathologists, and radiologists.The name GCT or osteoclastoma gives a false impression of a tumor comprising of proliferating osteoclasts or osteoclast precursors.The underlying mechanisms for excessive osteoclastogenesis are intriguing and GCT has served as an exciting disease model representing a paradigm of osteoclastogenesis for bone biologists.The modern interpretation of GCT is predominantly osteoclastogenic stromal cell tumors of mesenchymal origin.A diverse array of infl ammatory cytokines and chemokines disrupts osteoblastic differentiation and promotes the formation of excessive multi-nucleated osteoclastic cells.Pro-osteoclastogenic cytokines such as receptor activator of nuclear factor kappa-B ligand (RANKL), interleukin (IL)-6, and tumor necrosis factor (TNF) as well as monocyte-recruiting chemokines such as stromal cell-derived factor-1 (SDF-1) and monocyte chemoattractant protein (MCP)-1 participate in unfavorable osteoclastogenesis and bone destruction.This model represents a self-suffi cient osteoclastogenic paracrine loop in a localized area.Consistent with this paradigm, a recombinant RANK-Fc protein and bisphosphonates are currently being tried for GCT treatment in addition to surgical excision and conventional topical adjuvant therapies.