H3F3A mutation in giant cell tumour of the bone is detected by immunohistochemistry using a monoclonal antibody against the G34W mutated site of the histone H3.3 variant.

AIMS: Giant cell tumour of the bone (GCTB) is a neoplasm predominantly of long bones characterized by the H3F3A mutation G34W. Conventional diagnosis is challenged by the tumour's giant cell-rich morphology, which overlaps with other giant cell-containing lesions of the bone. Recently, a monoclonal antibody specific for the H3F3A mutation has been generated. Our aim was to test this antibody on a cohort of giant cell-containing lesions. METHODS AND RESULTS: We used the antibody for analysis of 22 H3F3A-mutated GCTB, including two patients with recurrences; for comparison we analysed a cohort of 36 H3F3A wild-type giant cell-rich lesions of the bone and soft tissue, containing one brown tumour, six aneurysmal bone cysts (ABC), six chondroblastomas, five non-ossifying-fibromas, two fibrous dysplasias, nine tenosynovial giant cell tumours, one giant cell-rich sarcoma and six osteosarcomas. Furthermore, among the 22 mutated cases, we included one GCTB with two recurrences and lung metastases; the patient was treated with the anti-receptor activator of nuclear factor κB (RANK) ligand denosumab. We show that all 22 H3F3A-mutated GCTB display strong nuclear H3.3 G34W staining in the neoplastic component, while the osteoclastic giant cells are negative. 36 H3F3A wild-type lesions are negative. The GCTB treated with denosumab revealed a reduction in the H3.3 G34W-positive tumour cells and a decrease in osteoclastic giant cells accompanied by matrix and osteoid formation. CONCLUSIONS: We conclude that positive H3.3 G34W staining is a specific and sensitive method for detection of H3F3A-mutated GCTB. Denosumab treatment leads to a pathomorphosis of the lesion characterized by matrix and osteoid producing H3.3 G34W-negative stromal cells.

Characterization of Three Novel H3F3A-mutated Giant Cell Tumor Cell Lines and Targeting of Their Wee1 Pathway.

The giant cell tumor of bone (GCTB) is a locally aggressive primary bone tumor that is composed of mononuclear stroma cells, scattered macrophages, and multinucleated osteoclast-like giant cells which cause pathologic osteolysis. The stroma cells represent the neoplastic population of the tumor and are characterized by the H3F3A mutation G34W. This point mutation is regarded as the driver mutation of GCTB. We have established three new stable H3F3A mutated GCTB cell lines: U-GCT1, U-GCT2, and U-GCT3M. MK-1775 is a Wee1-kinase inhibitor which has been used for blocking of sarcoma growth. In the cell lines we detected Wee1, Cdk1, Cyclin B1, H3K36me3, and Rrm2 as members of the Wee1 pathway. We analyzed the effect of MK-1775 and gemcitabine, alone and in combination, on the growth of the cell lines. The cell lines showed a significant reduction in cell proliferation when treated with MK-1775 or gemcitabine. The combination of both agents led to a further significant reduction in cell proliferation compared to the single agents. Immunohistochemical analysis of 13 GCTB samples revealed that Wee1 and downstream-relevant members are present in GCTB tissue samples. Overall, our work offers valuable new tools for GCTB studies and presents a description of novel biomarkers and molecular targeting strategies.