3.P.12 MORPHOLOGICAL AND IMMUNOPHENOTYPIC FEATURES OF METASTATIC GIANT CELL TUMOURS OF BONE: CLUES TO PATHOGENESIS

Abstract

Giant cell tumour of bone (GCTB) is a primary tumour of bone characterised by a proliferation of mononuclear stromal cells and infiltrating macrophages and osteoclast-like giant cells. GCTB has a variable and unpredictable course and can produce metastatic lesions, mostly in the lungs, in up to 3% of cases. Whether these represent tumour implants rather than true neoplastic secondaries is uncertain. In this study, we analysed morphological and immunophenotypic features of primary GCTBs which metastasised to the lung as well as the metastatic lesions themselves in order to determine if these would provide a clue as to the mechanism of lung metastasis in GCTB.

17 cases of primary GCTB which metastasised to the lung and the lung metastases in these cases were obtained from IOR, Bologna. Morphologically, primary tumours showed variable features, often containing both giant cell-rich and mononuclear stromal cell-rich areas. Mononuclear cells showed frequent mitotic activity and a degree of nuclear pleomorphism; none of the tumours showed cytological features of malignancy. The tumours were highly vascular and frequently contained dilated thin-walled blood vessels and large areas of haemorrhage. GCTB lung metastases were generally small and contained osteoclast-like giant cells and mononuclear stromal cells which showed typical mitotic activity; cytologically, the metastatic tumours were relatively bland and showed little nuclear pleomorphism. Expression of HLA-DR (an allele of which has been associated with a more aggressive GCTB phenotype) and smooth muscle actin (SMA) was noted in stromal cells in primary and secondary GCTBs; frequently, the same pattern of SMA expression was seen in both primary and secondary lesions. Osteoclasts were vitronectin receptor+, CD14-HLA-DR- in both primary and secondary GCTBs.

Our findings indicate that mononuclear stromal cells in lung metastases of GCTB often recapitulate the immunophenotype of the primary tumours from which they derive. Taken with the morphological finding that many primary GCTBs are highly vascular and contain areas of haemorrhage, it is possible that the lung “secondaries” of GCTB more likely represent tumour implants than true neoplastic metastases.