Morphological and immunophenotypic features of primary and metastatic giant cell tumour of bone

Giant cell tumour of bone (GCTB) is a primary tumour of bone that may rarely, in the absence of malignant cytological features, produce metastatic lesions, most commonly in the lungs. Whether these lung nodules represent true neoplastic secondaries or implants derived from the primary tumour is not certain. In this study, we have analysed the morphological and immunophenotypic features of 19 conventional GCTBs and corresponding lung nodules for expression of macrophage, osteoclast, proliferation and tumour-associated markers. A striking morphological feature of all GCTBs that produced lung secondaries was the presence of large areas of haemorrhage and thrombus formation; mononuclear and multinucleated cells of GCTB were frequently found within these areas of haemorrhage and thrombus. A similar pattern of CD14, CD33, HLA-DR and CD51 expression was seen in macrophages and giant cells in primary and secondary tumours. Smooth muscle actin expression was frequently noted in primary GCTBs that recurred and metastasised. No difference was seen in the expression of p53, p63, Ki-67, cyclin D1 or Bcl-2 in primary and secondary tumours. Our findings suggest that most lung nodules associated with primary conventional GCTBs are implants derived from tumour emboli formed in areas of haemorrhage and thrombus formation within the primary tumour.