Original contributionDiagnostic utility of histone H3.3 G34W, G34R, and G34V mutant-specific antibodies for giant cell tumors of bone☆
Introduction
Giant cell tumor of bone (GCTB) is an osteolytic tumor that usually develops in the metaphysis to epiphysis of a long bone or axial skeleton of young to middle-aged adults [1], [2]. GCTB may occur in the metaphysis without involving the epiphysis, particularly in children whose growth plates are still open. Histologically, GCTB is characterized by mononuclear stromal cells with round to spindle-shaped nuclei, mononuclear histiocytic cells and osteoclast-like multinucleated giant cells. Mononuclear stromal cells show an osteoblastic precursor phenotype, and these cells are thought to be neoplastic cells of GCTB, whereas mononuclear histiocytic cells and osteoclast-like multinucleated giant cells are considered non-neoplastic elements [3], [4].
GCTBs sometimes show secondary changes such as aneurysmal bone cyst (ABC) change, foamy histiocytic aggregates and reactive bone or osteoid formation. GCTB should be distinguished from various types of bone lesions with osteoclastic giant cells, including chondroblastoma, non-ossifying fibroma, brown tumor (hyperparathyroidism), giant cell reparative granuloma, primary ABC, and osteosarcoma, especially the giant cell–rich type.
Clinically, GCTB is a locally aggressive tumor with frequent local recurrence [1]. In addition, some cases of GCTB can show implantation or metastasis in the lung, in keeping with conventional GCTB histology. In rare cases, GCTB undergoes histologically malignant transformation. The malignant component corresponds to osteosarcoma, fibrosarcoma or, less frequently, undifferentiated high-grade pleomorphic sarcoma (UPS; formerly, malignant fibrous histiocytoma) [5], [6].
It has been shown that receptor activator of nuclear factor κ-B ligand (RANKL) and its receptor RANK axis play an important role in the development of GCTB (reviewed by Cowan and Singh [3]). RANKL expressed by mononuclear stromal cells binds to RANK on the surface of osteoclast-type multinucleated giant cells, leading to the activation and proliferation of these giant cells. Denosumab, an inhibitor of RANKL, has shown a promising anti-tumor effect for GCTB [7], [8]. According to previous reports, histological alterations of post-denosumab GCTBs include the depletion of osteoclastic giant cells, new bone formation, and spindle cell proliferation [9], [10], [11]. These appearances are distinct from the histology of conventional GCTB, and can be reminiscent of osteosarcoma or malignancy in GCTB, potentially leading to diagnostic difficulty.
Histone H3.3 is encoded by two genes located in different loci: H3F3A on chromosome 1 and H3F3B on chromosome 17. A previous study revealed the frequent H3F3A p.G34W mutation in GCTB and H3F3B p.K36 M mutation in chondroblastoma [12]. Subsequent studies demonstrated that approximately 85% to 95% of GCTBs harbor H3F3A p.G34W mutation, and a minor subset (each <1%-2%) have H3F3A p.G34L, p.G34M, p.G34R or p.G34V mutation [13], [14], [15]. Anti-H3.3 G34W mutant antibody is now available for immunohistochemical staining [16]. In the present study, we provide further evidence of the diagnostic utility of the H3.3 G34W mutant antibody for GCTB and its variant. We also examined the reliability of other markers for histone mutation variants: H3.3 G34R and G34V.
Section snippets
Case selection
We retrieved 75 lesions of GCTB and its variants from 52 patients registered in the files of the Department of Anatomic Pathology, Kyushu University, Japan. The 75 lesions consisted of primary conventional GCTBs (n = 51), recurrent conventional GCTBs (n = 13), post-denosumab GCTBs (n = 8), lung metastasis of conventional GCTB (n = 1), and secondary malignant GCTBs (n = 2). As a comparison, 122 cases of non-GCTB bone and joint lesions were examined. The specimens were obtained by biopsy, curettage or
H3.3 G34W, G34R and G34V expression in GCTBs and related lesions
Immunohistochemically, H3.3 G34W, G34R and G34V mutant protein expressions were detected in 47/51 (92%), 1/51 (2%) and 3/51 (6%) cases of primary conventional GCTBs, respectively (Table 1). All cases of recurrent conventional GCTB (n = 13), lung metastasis of conventional GCTB histology (n = 1), post-denosumab GCTB (n = 8) and secondary malignant GCTB (n = 2) were positive for H3.3 G34W and negative for H3.3 G34R and G34V. Expressions of these markers were detectable under all of the specimen
Diagnostic utility of H3.3 G34W/R/V immunohistochemistry for GCTB
There are accumulating data of histone H3.3 gene mutations in neoplasms, such as p.K27M and p.G34R/V in pediatric gliomas, p.G34W in GCTBs, and p.K36M in chondroblastomas [12], [17], [18]. Mutant-specific antibodies such as anti-K27M are currently available for the pathological diagnosis of brain tumors [19]. Amary et al reported that immunohistochemistry with an anti-K36M antibody may be a highly sensitive and specific marker for chondroblastoma [20]. Very recently, the same group reported
Conclusion
Our results suggest that H3.3 G34W, G34R and G34V mutant-specific antibodies are powerful diagnostic tools to identify GCTB and its variants and to distinguish non-GCTB lesions. The finding of H3.3 G34W mutant protein expression in bone-forming cells in post-denosumab GCTB suggests that neoplastic stromal cells of osteoblastic lineage may play a role in new bone formation.
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Conflicts of interest and source of funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.