RANK signalling in bone lesions with osteoclast-like giant cells

Aims: The interactions between the receptor activator of NF-kappa B (RANK), its ligand (RANKL), and the decoy receptor for RANKL, osteoprotegerin (OPG), play a pivotal role in promoting osteoclast differentiation and activation leading to bone resorption. Giant cell tumours, chondroblastomas, and aneurysmal bone cysts harbour osteolytic lesions containing osteoclast-like giant cells. We investigated the characteristics of the RANKL signalling pathway in each of these bone lesions. Methods: We evaluated 44 cases of giant cell tumour, 12 cases of chondroblastoma, six cases of aneurysmal bone cyst, and five cases of metastatic giant cell tumour (including paired primary giant cell tumours). We assessed RANK, RANKL, and OPG expression in chondroblastomas, giant cell tumours, and aneurysmal bone cysts using immunohistochemical methods. Results: Our findings revealed that RANK, RANKL, and OPG expression differed significantly among disease types. Giant cells of chondroblastomas showed significantly higher RANK expression than the giant cells of giant cell tumours and aneurysmal bone cysts; similarly, stromal cells of chondroblastomas showed significantly higher OPG expression than the stromal cells of giant cell tumours and aneurysmal bone cysts. Furthermore, giant cells of giant cell tumours expressed significantly more RANK than the giant cells of aneurysmal bone cysts. Conclusions: The expression of RANK, RANKL, and OPG in osteoclast-like giant cells differs significantly by disease; OPG expression differs significantly between giant cell tumours and chondroblastomas.