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

Introduction Giant cell tumor of bone (GCTOB) 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 (including one solid variant), 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 extent 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, which is considerably more than any other giant cell-rich lesion. However, positive staining for p63 is not specific for GCTOB 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 relatively specific marker for discriminating GCTOB from other types of giant cell-rich lesions. We suggest a combined scoring method for p63 IHC staining interpretation in GC-rich lesions, considering both intensity and extent of reaction, with a 2+ cut off as a more accurate marker for the diagnosis of GCTOB within the appropriate clinical context. © 2016 Elsevier Gmb