P63 expression as a biomarker discriminating giant cell tumor of bone from other giant cell-rich bone lesions

Introduction: Giant cell tumor of bone is a locally aggressive neoplasm that accounts for 5% of all primary bone tumors. This tumor overlaps in histopathologic and radiographic presentations with different malignant, benign, and metabolic giant cell-rich lesions. The purpose of this study is to evaluate p63 expression status in giant cell tumor of bone in comparison with other giant cell-rich lesions. Materials and Methods: In a cross-sectional study we examined immunohistochemical expression of p63 in a series of 100 giant cell-rich bone lesions, including 31 giant cell tumors of bone, 14 osteosarcomas (Including 3 giant cell-rich variants), 18 aneurysmal bone cysts, 8 non-ossifying fibromas, 17 chondroblastomas, 8 tenosynovial giant cell tumors, and 4 brown tumors. Results: Immunohistochemical analysis showed p63 nuclear expression in 96.8% of giant cell tumors of bone, 14.3% of osteosarcomas, 50% of non-ossifiying fibromas, 22.2% of aneurysmal bone cysts, 68.7% of chondroblastomas, 75.0% of brown tumors and none of the tenosynovial giant cell tumors. Taking into account the intensity of staining, we identified strong staining in 48.4% of giant cell tumors of bone, 35.3% of chondroblastomas and 7.1% of osteosarcomas (in 2 cases which were both giant cell-rich variants). Considering extension of staining, extensive staining was only observed in 58.0% of giant cell tumors of bone, 23.5% of chondroblastomas and 14.3% of osteosarcomas.Conclusion: A large number of giant cell tumors of bone (96.8%) are positive for p63 that is considerably more than any other giant cell-rich lesion. However, positive staining for p63 is not specific for giant cell tumor of bone and may be seen in other lesions such as chondroblastoma, non-ossifying fibroma, Brown tumor, and giant cell-rich osteosarcoma. p63 is a sensitive(96.8%) and rather specificmarker for discriminating giant cell tumor of bone from other types of giant cell-rich lesions. We suggest a combined scoring system for p63 IHC staining interpretation in GC-rich lesions, considering both intensity and extension of reaction, with a 1+ cut off as a more accurate marker for the diagnosis of GCTOB