Diagnostic value of H3F3A mutations in giant cell tumour of bone compared to osteoclast-rich mimics

Genomic Insights Into High-Grade Infarct-Associated Bone Sarcomas

Sarcomas rarely develop in bones previously compromised by infarcts. These infarct-associated sarcomas often present as undifferentiated pleomorphic sarcomas (UPS), and their genetic characteristics are poorly understood. High-grade UPS of bone are typically treated with a combination of surgery and chemotherapy, similar to osteosarcoma. We conducted a detailed clinicopathologic and genomic analysis of 6 cases of intraosseous sarcomas arising from histologically and radiographically confirmed bone infarcts. We analyzed 523 genes for sequence-level mutations using next-generation sequencing with the TruSight Oncology 500 panel and utilized whole-genome single nucleotide polymorphism Microarray (OncoScan CNV) to detect copy number alterations and loss of heterozygosity (LOH). Genomic instability was assessed through homologous recombination deficiency (HRD) metrics, incorporating LOH, telomeric allelic imbalance, and large-scale state transitions. Fluorescence in situ hybridization and immunohistochemistry validated the findings. The cohort included 3 men and 3 women, with a median age of 70 years, and tumors located in the femur and tibia. Five of the 6 patients developed distant metastases. Treatment involved surgery and chemotherapy or immune checkpoint inhibitors. Genomic analysis revealed significant complexity and high HRD scores, ranging from 32 to 57 (with a cutoff of 32). Chromosome 12 alterations, including segmental amplification or chromothripsis, were observed in 4 cases. Notably, MDM2 amplification, confirmed by fluorescence in situ hybridization, was detected in 2 cases. Homozygous deletion of CDKN2A/B was observed in all six cases. Tumor mutational burden levels ranged from 2.4 to 7.9 mutations per megabase. Notable pathogenic mutations included H3-3A mutations (p.G35R and p.G35W), and mutations in HRAS, DNMT3A, NF2, PIK3CA, POLE, and TP53, each in one case. These results suggest that high-grade infarct-associated sarcomas of bone, whereas sharing high levels of structural variations with osteosarcoma, may exhibit potentially less frequent TP53 mutations and more common CDKN2A/B deletions. This points to the possibility that the mutation spectrum and disrupted pathways could be distinct from conventional osteosarcoma.

Recent advances in molecular profiling of bone and soft tissue tumors

The molecular characterization of soft tissue and bone tumors is a rapidly evolving field that has changed the perspective of how these tumors are diagnosed today. Morphology and clinico-radiological context still represent the cornerstone of diagnostic considerations but are increasingly complemented by molecular data that aid in objectifying and confirming the classification. The spectrum of analyses comprises mutation or gene fusion specific immunohistochemical antibodies, fluorescence in situ hybridization, DNA and RNA sequencing as well as CpG methylation profiling. This article provides an overview of which tools are presently available to characterize bone and soft tissue neoplasms molecularly, what limitations should be considered, and what conclusions can be drawn from the individual findings.

Pathogenetic and molecular classifications of soft tissue and bone tumors: A 2024 update

Soft tissue and bone tumors comprise a wide category of neoplasms. Their diversity frequently raises diagnostic challenges, and therapeutic options are continuously developing. The therapeutic success rate and long-term prognosis of patients have improved substantially due to new advances in immunohistochemical and molecular biology techniques. A fundamental contribution to these achievements has been the study of the tumor microenvironment and the reclassification of new entities with the updating of the molecular pathogenesis in the revised 5th edition of the Classification of Soft Tissue Tumors, edited by the World Health Organization. The proposed molecular diagnostic techniques include the well-known in situ hybridization and polymerase chain reaction methods, but new techniques such as copy-number arrays, multiplex probes, single-nucleotide polymorphism, and sequencing are also proposed. This review aims to synthesize the most recent pathogenetic and molecular classifications of soft tissue and bone tumors, considering the major impact of these diagnostic tools, which are becoming indispensable in clinicopathological practice.

Giant cell tumor of bone and secondary osteoarthritis

Giant cell tumor of bone is a commonly encountered aggressive epiphyseal bone tumor, most often treated surgically. The natural history and presentation are classically described but the histopathology is poorly understood. Intralesional curettage is the mainstay of treatment, but there is significant variation in the use of adjuvant and cavity filling modalities. No gold standard has been agreed upon for treatment, and a variety of techniques are currently in use. Given its location, secondary osteoarthritis is a known long-term complication. This review examines the natural history of giant cell tumors, treatment options and complications, and subsequent development of osteoarthritis. Arthroplasty is usually indicated for secondary osteoarthritis although data is limited on its efficacy. Further directions will likely center on improved pharmacological treatments as well as improved arthroplasty techniques.

Keratin-Positive Giant Cell-Rich Tumor: A Review and Update

Keratin-positive giant cell-rich tumor (KPGCT) is an extremely rare and recently described mesenchymal neoplasm that occurs in both soft tissue and bone, frequently found in young women. It has locally recurrent potential if incompletely excised but low risk for metastasis. KPGCT is histologically similar to conventional giant cell tumors of soft tissue but shows the presence of keratin-positive mononuclear cells. Interestingly, KPGCT also shares some morphological features with xanthogranulomatous epithelial tumors. These two tumors have recently been shown to harbor an HMGA2-NCOR2 fusion, arguing in favor of a single entity. Surgery is the treatment of choice for localized KPGCT. Therapeutic options for advanced or metastatic disease are unknown. This review provides an overview of the current knowledge on the clinical presentation, pathogenesis, histopathology, and treatment of KPGCT. In addition, we will discuss the differential diagnosis of this emerging entity.

Giant Cell Tumor of Soft Tissue: An Updated Review

Giant cell tumor of soft tissue (GCTST) is a locally aggressive mesenchymal neoplasm of intermediate malignancy that predominantly occurs in the superficial soft tissue of the extremities. It is histologically similar to a giant cell tumor of bone (GCTB) and shows a mixture of round to oval mononuclear cells and osteoclast-like multinucleated giant cells. Currently, immunohistochemistry plays a very limited role in the diagnosis of GCTST. Primary or secondary malignant GCTST has recently been described and tumors exhibiting high-grade histological features demonstrate higher rates of distant metastasis. GCTST lacks the H3-3A gene mutations that are identified in the vast majority of GCTBs, suggesting a different pathogenesis. Surgery is the standard treatment for localized GCTST. Incomplete surgical resection is usually followed by local recurrence. Radiation therapy may be considered when the close proximity of critical structures prevents microscopically negative surgical margins. The systemic treatment options for advanced or metastatic disease are very limited. This review provides an updated overview of the clinicoradiological features, pathogenesis, histopathology, and treatment for GCTST. In addition, we will discuss the differential diagnosis of this peculiar neoplasm.

Histones and their practical application in bone tumors: Do I always need them?

Historically, the diagnosis of giant cell-rich neoplasms arising in bone has been challenging owing to overlapping clinical and radiographic findings resulting in the difficult separation of several neoplasms, particularly when biopsy material is limited. However, with the discovery of the driver histone mutations in giant cell tumor of bone (GCTB) and chondroblastoma, as well as USP6 rearrangements in aneurysmal bone cyst, pathologists now have objective ancillary tools to aid in the separation of several histologically similar giant cell-rich neoplasms. Furthermore, the recognition of histone mutations has allowed pathologists to revisit several entities, such as "malignant chondroblastoma," and furthered our understanding of phenomena such as "aneurysmal bone cyst-like change," formerly recognized as "secondary aneurysmal bone cyst." Herein, the evolution of testing for histone mutations in bone tumors is considered; the sensitivity and specificity of the histone antibodies is reviewed; and a practical guide for the use of these ancillary tests is offered.

Keratin-Positive Giant Cell-Rich Tumor of Bone Harboring an HMGA2::NCOR2 Fusion: Two Cases, Including a Patient With Metastatic Disease, and Review of the Literature

Giant cell-rich lesions of bone represent a heterogeneous group of entities which classically include giant cell tumor of bone, aneurysmal bone cyst, nonossifying fibroma, and Brown tumor of hyperparathyroidism. A recently described subset of giant cell-rich tumors involving bone and soft tissue has been characterized by recurrent HMGA2::NCOR2 fusions and keratin expression. The overlapping clinical, radiographic, and morphological features of these giant cell-rich lesions provide a unique diagnostic challenge, particularly on biopsy. We present 2 additional cases of keratin-positive giant cell-rich tumor of bone with HMGA2::NCOR2 fusions, including 1 patient who developed metastatic disease.

Treatment of Clival Giant Cell Tumor: A Case Report and Literature Review

Giant cell tumors (GCTs) are locally aggressive primary bone tumors of osteoclast-like cells. Most GCTs occur within the long bones, and primary GCTs involving the clivus are extremely rare. We present the case of an 18-year-old boy with binocular horizontal diplopia with an insidious onset who was found to have a hypointense enhancing mass involving the clivus and left side dorsum sellae on magnetic resonance images. The tumor was completely resected via an endoscopic endonasal transclival approach, and histopathologic examination via immunohistochemistry indicated a GCT. The patient's left abducens nerve palsy improved slightly after surgery. Because of the rarity of GCTs, there is no consensus about the definitive treatment protocol. However, we suggest that gross total resection is the treatment of choice, and denosumab plays a critical role in patients with subtotal resection.

Diagnosis and monitoring denosumab therapy of giant cell tumors of bone: radiologic-pathologic correlation

OBJECTIVE

To determine the value of CT and dynamic contrast-enhanced (DCE-)MRI for monitoring denosumab therapy of giant cell tumors of bone (GCTB) by correlating it to histopathology.

MATERIALS AND METHODS

Patients with GCTB under denosumab treatment and monitored with CT and (DCE-)MRI (2012-2021) were retrospectively included. Imaging and (semi-)quantitative measurements were used to assess response/relapse. Tissue samples were analyzed using computerized segmentation for vascularization and number of neoplastic and giant cells. Pearson's correlation/Spearman's rank coefficient and Kruskal-Wallis tests were used to assess correlations between histopathology and radiology.

RESULTS

Six patients (28 ± 8years; five men) were evaluated. On CT, good responders showed progressive re-ossification (+7.8HU/month) and cortical remodeling (woven bone). MRI showed an SI decrease relative to muscle on T1-weighted (-0.01 A.U./month) and on fat-saturated T2-weighted sequences (-0.03 A.U./month). Time-intensity-curves evolved from a type IV with high first pass, high amplitude, and steep wash-out to a slow type II. An increase in time-to-peak (+100%) and a decrease in Ktrans (-71%) were observed. This is consistent with microscopic examination, showing a decrease of giant cells (-76%), neoplastic cells (-63%), and blood vessels (-28%). There was a strong statistical significant inverse correlation between time-to-peak and microvessel density (ρ = -0.9, p = 0.01). Significantly less neoplastic (p = 0.03) and giant cells (p = 0.04) were found with a time-intensity curve type II, compared to a type IV. Two patients showed relapse after initial good response when stopping denosumab. Inverse imaging and pathological findings were observed.

CONCLUSION

CT and (DCE-)MRI show a good correlation with pathology and allow adequate evaluation of response to denosumab and detection of therapy failure.

Giant Cell Tumor of the Acromion: Case Report and Literature Review

BACKGROUND/AIM

Giant cell tumor of bone (GCTB) is a locally aggressive neoplasm that typically occurs in the ends (epiphyses) of long bones of young adults. Flat bones are uncommon sites of involvement. Herein, we describe an unusual case of pathologically proven GCT of the acromion.

CASE REPORT

The patient was a 39-year-old woman with no history of trauma who presented with a 3-month history of right posterior shoulder pain. Physical examination revealed mild swelling and tenderness in the posterior aspect of the right shoulder. Plain radiograph showed a purely lytic lesion, suggestive of a bone tumor. Computed tomography demonstrated an intraosseous lytic lesion with associated cortical thinning and lack of periosteal reaction. On magnetic resonance imaging, the lesion exhibited slightly higher signal intensity compared to skeletal muscle on T1-weighted sequences and heterogeneous high signal intensity on T2-weighted sequences. Strong enhancement was observed following gadolinium administration. The lesion was treated by extensive curettage with adjuvant therapy comprising ethanol and the remaining cavity was filled with polymethylmethacrylate bone cement. Histologically, the lesion was composed of round or spindle-shaped mononuclear cells admixed with numerous osteoclast-like giant cells. Immunohistochemically, the mononuclear neoplastic cells were diffusely positive for H3.3 G34W. The patient was asymptomatic and there was no evidence of local recurrence or distant metastasis 5 months after surgery.

CONCLUSION

Although rare, acromial GCTB should be considered in the differential diagnosis of posterior shoulder pain, especially in young and early middle-aged adults.

DNA methylation profile discriminates sporadic giant cell granulomas of the jaws and cherubism from their giant cell-rich histological mimics

Sporadic giant cell granulomas (GCGs) of the jaws and cherubism-associated giant cell lesions share histopathological features and microscopic diagnosis alone can be challenging. Additionally, GCG can morphologically closely resemble other giant cell-rich lesions, including non-ossifying fibroma (NOF), aneurysmal bone cyst (ABC), giant cell tumour of bone (GCTB), and chondroblastoma. The epigenetic basis of these giant cell-rich tumours is unclear and DNA methylation profiling has been shown to be clinically useful for the diagnosis of other tumour types. Therefore, we aimed to assess the DNA methylation profile of central and peripheral sporadic GCG and cherubism to test whether DNA methylation patterns can help to distinguish them. Additionally, we compared the DNA methylation profile of these lesions with those of other giant cell-rich mimics to investigate if the microscopic similarities extend to the epigenetic level. DNA methylation analysis was performed for central (n = 10) and peripheral (n = 10) GCG, cherubism (n = 6), NOF (n = 10), ABC (n = 16), GCTB (n = 9), and chondroblastoma (n = 10) using the Infinium Human Methylation EPIC Chip. Central and peripheral sporadic GCG and cherubism share a related DNA methylation pattern, with those of peripheral GCG and cherubism appearing slightly distinct, while central GCG shows overlap with both of the former. NOF, ABC, GCTB, and chondroblastoma, on the other hand, have distinct methylation patterns. The global and enhancer-associated CpG DNA methylation values showed a similar distribution pattern among central and peripheral GCG and cherubism, with cherubism showing the lowest and peripheral GCG having the highest median values. By contrast, promoter regions showed a different methylation distribution pattern, with cherubism showing the highest median values. In conclusion, DNA methylation profiling is currently not capable of clearly distinguishing sporadic and cherubism-associated giant cell lesions. Conversely, it could discriminate sporadic GCG of the jaws from their giant cell-rich mimics (NOF, ABC, GCTB, and chondroblastoma).

Pediatric Gnathic Bony and Mesenchymal Tumors

Evaluation of bone pathology within the head and neck region, particularly the gnathic bonesis is complex, demonstrating unique pathologic processes. In part, this variation is due to odontogenesis and the embryological cells that may be involved, which can contribute to disease development and histologic variability. As with any boney pathosis, the key is to have clinical correlation, particularly with radiographic imaging prior to establishing a definitive diagnosis. This review will cover those entities that have a predilection for the pediatric population, and while it is not all inclusive, it should serve as a foundation for the pathologist who is evaluating bony lesions involving the craniofacial skeleton.

(B)On(e)-cohistones and the epigenetic alterations at the root of bone cancer

Identification of mutations in histones in a number of human neoplasms and developmental syndromes represents the most compelling evidence to date for a causal role of epigenetic perturbations in human disease. In most cases, these mutations have gain of function properties that cause deviation from normal developmental processes leading to embryo defects and/or neoplastic transformation. These exciting discoveries represent a step-change in our understanding of the role of chromatin (dys)regulation in development and disease. However, the mechanisms of action of oncogenic histone mutations (oncohistones) remain only partially understood. Here, we critically assess existing literature on oncohistones focussing mainly on bone neoplasms. We show how it is possible to draw parallels with some of the cell-autonomous mechanisms of action described in paediatric brain cancer, although the functions of oncohistones in bone tumours remain under-investigated. In this respect, it is becoming clear that histone mutations targeting the same residues display, at least in part, tissue-specific oncogenic mechanisms. Furthermore, it is emerging that cancer cells carrying oncohistones can modify the surrounding microenvironment to support growth and/or alter differentiation trajectories. A better understanding of oncohistone function in different neoplasms provide potential for identification of signalling that could be targeted therapeutically. Finally, we discuss some of the main concepts and future directions in this research area, while also drawing possible connections and parallels with other cancer epigenetic mechanisms.

Giant-cell-poor giant cell tumor of bone: report of two cases and literature review

Giant cell tumor of bone (GCTB) is a locally aggressive tumor that shows predilection for the metaphysis/epiphysis of long bones, with an incidence of 4-5% of primary bone tumors. GCTB shows two main populations of cells: mononuclear cells and non-neoplastic multi-nucleated giant cells, with or without fibrous background. On the other hand, giant-cell-poor GCTB are rare with only few reports in the literature. These cases offer a diagnostic challenge, given the absence of giant cells and such cases have consistently been shown to harbor the H3F3A gene mutation by sequencing. The H3.3 G34W mutation-specific monoclonal antibody has shown high specificity in the diagnosis of GCTB. Two cases of giant-cell-poor GCTB are presented in this study, in which giant cells were absent or sparse and the diagnosis of GCTB was confirmed by the expression of H3.3 G34W monoclonal antibody in the mononuclear cells by immunohistochemistry. Whether this represents a histologic variant of GCTB or partial involution of GCTB is not yet fully understood; however, an immune response, infectious/inflammatory reaction, and/or anti-tumor cytokine production have been purported to be factors inciting disease regression in GCTB.

Histomorphometric Analysis of 38 Giant Cell Tumors of Bone after Recurrence as Compared to Changes Following Denosumab Treatment

Giant cell tumor of bone (GCTB) is an osteolytic tumor driven by an H3F3A-mutated mononuclear cell with the accumulation of osteoclastic giant cells. We analyzed tissue from 13 patients with recurrence and 25 patients with denosumab therapy, including two cases of malignant transformation. We found a decrease in the total number of cells (p = 0.03), but not in the individual cell populations when comparing primary and recurrence. The patients treated with denosumab showed induction of osteoid formation increasing during therapy. The total number of cells was reduced (p < 0.0001) and the number of H3F3A-mutated tumor cells decreased (p = 0.0001), while the H3F3A wild-type population remained stable. The KI-67 proliferation rate dropped from 10% to 1% and Runx2- and SATB2-positive cells were reduced. The two cases of malignant transformation revealed a loss of the H3F3A-mutated cells, while the KI-67 rate increased. Changes in RUNX2 and SATB2 expression were higher in one sarcoma, while in the other RUNX2 was decreased and SATB2-positive cells were completely lost. We conclude that denosumab has a strong impact on the morphology of GCTB. KI-67, RUNX2 and SATB2 expression differed depending on the benign or malignant course of the tumor under denosumab therapy.

Chondroblastoma of foot bones; a clinicopathological study of 29 cases confirming the diagnostic utility of H3K36M and H3G34W antibodies at an uncommon site

OBJECTIVE

Chondroblastoma (CB) is a benign cartilaginous bone neoplasm which commonly occurs in long bones of adolescents. CB can uncommonly involve foot. Its mimics include both benign and malignant lesions. H3K36M immunohistochemical (IHC) stain is a helpful tool for establishing the diagnosis of CB in such challenging situations. In addition, H3G34W IHC stain helps to rule out giant cell tumor which is the closest differential of CB. Our objective was to describe the clinicopathological features and frequencies of H3K36M, H3G34W and SATB2 IHC stains in CB of foot.

MATERIALS AND METHODS

We reviewed H&E slides and blocks of 29 cases diagnosed as "chondroblastoma" of foot at our institutions.

RESULTS

Patient's age ranged from 6 to 69 (mean: 23.3 and median: 23) years. Males were almost 5 times more commonly affected than females. Talus and calcaneum were involved in 13 (44.8 %) cases each. Microscopically, tumors were composed of polygonal mononuclear cells and multinucleated giant cells and chondroid matrix. Other histological features included aneurysmal bone cyst-like (ABC-like) change (44.8 %), osteoid matrix (31 %), chicken-wire calcification (20.7 %), and necrosis (10.3 %). H3K36M was expressed in 100 % and SATB2 in 91.7 % cases. H3G34W was negative in all cases, where performed. One out of 11 patients with follow up information developed local recurrence after 48 months.

CONCLUSION

CB in foot occur at an elder age and show more frequent ABC-like changes as compared to long bones. Males are affected ~5:1 as compared to 2:1 in long bones. H3K36M are H3G34W are extremely useful diagnostic markers for CB, especially elderly (aged or higher) patients and we report the largest series of foot CB cases confirmed by immunohistochemistry.

Giant Cell Tumor of Bone Without Giant Cells with a Long Clinical Course: A Case Report

Giant cell tumor of bone (GCTB) consists of a mixture of neoplastic mononuclear cells and non-neoplastic cells, including polynuclear giant cells. Recently, with the spread of the immunohistochemical staining marker H3.3 G34W corresponding to specific genetic abnormalities, the histological diversity of GCTB has been recognized. GCTB without giant cells is uncommon, although it has also been reported previously. Herein, we describe a 45-year-old man with GCTB without giant cells who was successfully diagnosed using H3.3 G34W immunohistochemistry. Other unusual findings in GCTB that were identified in this patient include bone and osteoid formation with a long clinical course of 13 years. We also compared the histological findings of the current patient to those who received denosumab therapy.

Inhibition of RANKL Expression in Osteocyte-like Differentiated Tumor Cells in Giant Cell Tumor of Bone After Denosumab Treatment

Giant cell tumors of bone (GCTBs) are locally aggressive tumors with the histological features of giant cells and stromal cells. Denosumab is a human monoclonal antibody that binds to the cytokine receptor activator of nuclear factor-kappa B ligand (RANKL). RANKL inhibition blocks tumor-induced osteoclastogenesis, and survival, and is used to treat unresectable GCTBs. Denosumab treatment induces osteogenic differentiation of GCTB cells. In this study, the expression of RANKL, special AT-rich sequence-binding protein 2 (SATB2, a marker of osteoblast differentiation), and sclerostin/SOST (a marker of mature osteocytes) was analyzed before and after treatment with denosumab in six cases of GCTB. Denosumab therapy was administered a mean of five times over a mean 93.5-day period. Before denosumab treatment, RANKL expression was observed in one of six cases. After denosumab therapy, spindle-like cells devoid of giant cell aggregation were RANKL-positive in four of six cases. Bone matrix-embedded osteocyte markers were observed, although RANKL was not expressed. Osteocyte-like cells were confirmed to have mutations, as identified using mutation-specific antibodies. Our study results suggest that treatment of GCTBs with denosumab results in osteoblast-osteocyte differentiation. Denosumab played a role in the suppression of tumor activity via inhibition of the RANK-RANKL pathway, which triggers osteoclast precursors to differentiate into osteoclasts.

Bone and soft tissue tumors: clinicoradiologic-pathologic molecular-genetic correlation of novel fusion spindled, targetable-ovoid, giant-cell-rich, and round cell sarcomas

BACKGROUND

New entities in the classification of bone and soft tissue tumors have been identified by use of advanced molecular-genetic techniques, including next-generation sequencing. Clinicoradiologic and pathologic correlation supports diagnostic classification.

METHODS

Tumors from four morphologically grouped areas are selected to enhance diagnosis and awareness among the multidisciplinary team. These include select round cell tumors, spindle cell tumors, targetable tyrosine kinase/RAS::MAPK pathway-ovoid (epithelioid to spindled) tumors, and giant-cell-rich tumors of bone and soft tissue.

RESULTS

Round cell tumors of bone and soft tissue include prototypical Ewing sarcoma, newer sarcomas with BCOR genetic alteration and CIC-rearranged, as well as updates on FUS/EWSR1::NFATc2, an EWSR1 non-ETS tumor that is solid with additional amplified hybridization signal pattern of EWSR1. This FUS/EWSR1::NFATc2 fusion has now been observed in seemingly benign to low-grade intraosseous vascular-rich and simple (unicameral) bone cyst tumors. Select spindle cell tumors of bone and soft tissue include rhabdomyosarcoma with FUS/EWSR1::TFCP2, an intraosseous high-grade spindle cell tumor without matrix. Targetable tyrosine-kinase or RAS::MAPK pathway-tumors of bone and soft tissue include NTRK, ALK, BRAF, RAF1, RET, FGFR1, ABL1, EGFR, PDGFB, and MET with variable ovoid myopericytic to spindled pleomorphic features and reproducible clinicopathologic and radiologic clues to their diagnosis. Giant-cell-rich tumors of bone, joint, and soft tissue are now respectively characterized by H3F3A mutation, CSF1 rearrangement (targetable), and HMGA2::NCOR2 fusion.

CONCLUSION

This article is an update for radiologists, oncologists, surgeons, and pathologists to recognize these novel ovoid, spindled, giant-cell-rich, and round cell tumors, for optimal diagnostic classification and multidisciplinary team patient care.

Giant cell tumor of bone with H3F3B mutation: A case report

RATIONALE

Giant cell tumor of bone is a locally aggressive and rarely metastasizing neoplasm that typically affects the ends of long bones or the axial skeleton of young to middle-aged adults. As many as 69% to 100% of giant cell tumors harbor H3F3A gene mutations, while H3F3B gene mutations have rarely been reported.

PATIENT CONCERNS

A 53-year-old male patient who underwent right distal femoral tumor resection.

DIAGNOSES

Preoperative CT plain scan indicated giant cell tumor of bone with pathological fracture. Laboratory findings were as follows: serum calcium was 2.23 mmol/L (reference range: 2.1-2.55 mmol/L) and serum phosphorus was 1.35 mmol/L (reference range: 0.81-1.45 mmol/L).

INTERVENTIONS

The histological morphology showed the typical features of a conventional GCT. The immunoprecipitation analysis results were as follows: H3.3G34W(-), H3.3G34R(-), H3.3G34V(-), and H3K36M(-). Sanger sequencing showed that the H3F3A and H3F3B gene mutations were wild type. The high-throughput gene sequencing results revealed the H3F3B gene mutations H3.3p.Gly35Trp and H3.3p.Val36Leu.

OUTCOMES

The patient was stable with no recurrence in 12 months follow-up.

LESSONS

Giant cell tumor of bone with H3F3B gene mutations is extremely rare. In the pathological diagnosis of bone tumors, we need to analyze clinical presentation, imaging features, histology, immunophenotype, and cytogenetic/molecular alterations, in order to get a correct diagnosis.

[Changes in the WHO classification (2020) of soft tissue tumors]

The article provides an overview of the main changes in the current (2020) WHO classification of soft tissue tumors, as well as selected updates that have occurred since the release of the classification.

Chondroblastoma: clinicopathological analyses of 307 cases from a single institution in China and the diagnostic value of the H3F3 K36M mutant antibody

AIMS

To elucidate the clinicopathological features and the diagnostic value of mutation specific antibody H3F3 K36M of chondroblastoma (CB) in China.

METHODS

Clinicopathological profiles were retrieved, and immunohistochemistry was performed on 185 CB specimens and the control group.

RESULTS

Our series included 307 patients with a mean age of 22.1 years. Long tubular bones (63.8%, 196/307) were most commonly involved, followed by short bones of the hands and feet (22.1%, 68/307), sesamoid bones (8.1%, 25/307), flat bones and irregular bones (5.9%, 18/307). The most commonly involved site was the proximal femur, followed by distal femur, proximal humerus and calcaneus. The average age in the long bones group (20.3 years) was significantly younger than the short bones group (24.9 years) (p<0.001), sesamoid bones group (24.4 years) (p=0.02) and flat bones and irregular bones group (29.1 years) (p<0.001). Microscopically, aneurysmal bone cyst-like change (63.6%, 117/184), necrosis (43.5%, 80/184) and chicken-wire calcification (26.1%, 48/184) were variably noted. In rare cases, cortical destruction, soft tissue and lymphovascular invasion were identified. Positive immunoreaction with H3F3 K36M was examined in all non-decalcified, all EDTA decalcified, 87.1% hydrochloric acid (HCl) decalcified CB samples and the high-grade sarcoma secondary to CB, but not the control group.

CONCLUSIONS

CB usually involves the long tubular bones in younger age group. H3F3 K36M can identify K36M mutation with 100% specificity and 100% sensitivity in non-decalcified and EDTA decalcified samples, more than 80% sensitivity in HCl decalcified samples. Virtually, all CBs harbour an H3K36M mutation.

Diagnostic value of H3F3A mutation and clinicopathological features of giant cell tumours in non-long bones

Aims

A histone H3F3A (H3.3) mutation involving a substitution in H3.3 G34 recently has been reported in GCTB within the frequency range (from 69 % to 96 %) and is a helpful diagnostic indicator of GCTB. However, the relationship between H3F3A mutations and the clinicopathological feature of GCTB involving non-long bones (irregular bones and small bones) is unclear.

Methods and results

H3F3A mutations were observed in a cohort of specimens (230 samples of GCTB) using immunohistochemistry and Sanger sequencing. The relationship between H3F3A mutations and the clinicopathological characteristics of patients with GCTB occurring in the non-long bones of the appendicular skeleton was investigated. No significant difference between H3F3A mutations in GCTB arising in non-long bones and the classic sites was found (P = 0.483). GCTB in non-long bones occurred more common in female (31/49, 63.3 %) than in male patients (P = 0.016). GCTB with H3.3 G34L/V/R mutation occurred more often in younger patients compared with those with H3.3 G34W mutation (P = 0.009). The majority of GCTB with soft tissue extension developed in irregular bones but not in small bones (P = 0.061). The H3.3 G34L/V/R mutations rate (7/45) in the non-long bones was significantly higher than that in long bones. The recurrence rate of the GCTB in long bones and non-long bones was 23.3 % (45/193) including 43 cases with local recurrene and 2 cases with lung metastasis. No recurrence occurred in cases with G34V/L/R mutations.

Conclusions

H3F3A was an effective diagnostic marker for GCTB of the non-long bones. The younger patients with GCTB of the non-long bones harboured H3.3 G34L/V/R mutations and may had a female preference and rarely recurrent.

ACE2 polymorphisms impact COVID-19 severity in obese patients

A strong association between obesity and COVID-19 complications and a lack of prognostic factors that explain the unpredictable severity among these patients still exist despite the various vaccination programs. The expression of angiotensin converting enzyme 2 (ACE2), the main receptor for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), is enhanced in obese individuals. The occurrence of frequent genetic single nucleotide polymorphisms (SNPs) in ACE2 is suggested to increase COVID-19 severity. Accordingly, we hypothesize that obesity-associated ACE2 polymorphisms increase the severity of COVID-19. In this study, we profiled eight frequently reported ACE2 SNPs in a cohort of lean and obese COVID-19 patients (n = 82). We highlight the significant association of rs2285666, rs2048683, rs879922, and rs4240157 with increased severity in obese COVID-19 patients as compared to lean counterparts. These co-morbid-associated SNPs tend to positively correlate, hence proposing possible functional cooperation to ACE2 regulation. In obese COVID-19 patients, rs2285666, rs879922, and rs4240157 are significantly associated with increased blood nitrogen urea and creatinine levels. In conclusion, we highlight the contribution of ACE2 SNPs in enhancing COVID-19 severity in obese individuals. The results from this study provide a basis for further investigations required to shed light on the underlying mechanisms of COVID-19 associated SNPs in COVID-19 obese patients.

Genetic analysis of CFH and MCP in Egyptian patients with immune-complex proliferative glomerulonephritis

Glomerulonephritis (GN) is a complex disease with intricate underlying pathogenic mechanisms. The possible role of underlying complement dysregulation is not fully elucidated in some GN subsets, especially in the setting of autoimmunity or infection. In the current study, diagnosed cases of lupus nephritis (LN) and post-infectious GN (PIGN) were recruited for molecular genetic analysis and targeted next-generation DNA sequencing was performed for two main complement regulating genes: in the fluid phase; CFH, and on tissue surfaces; MCP. Three heterozygous pathogenic variants in CFH (Q172*, W701*, and W1096*) and one likely pathogenic heterozygous variant in MCP (C223R) have been identified in four of the studied LN cases. Additionally, among the several detected variants of uncertain significance, one novel variant (CFH:F614S) was identified in 74% of the studied LN cases and in 65% of the studied PIGN cases. This variant was detected for the first time in the Egyptian population. These findings suggest that subtle mutations may be present in complement regulating genes in patients with immune-complex mediated category of GN that may add to the disease pathogenesis. These findings also call for further studies to delineate the impact of these gene variants on the protein function, the disease course, and outcome.

Imaging Features of Craniofacial Giant Cell Granulomas: A Large Retrospective Analysis from a Tertiary Care Center

BACKGROUND AND PURPOSE

Craniofacial giant cell granulomas are rare lesions with varied appearances on imaging. We aimed to describe the imaging features of giant cell granulomas of the craniofacial bones.

MATERIALS AND METHODS

A retrospective analysis of the clinical features and imaging findings of 20 histopathology-proved cases of craniofacial giant cell granulomas, dating from 2006 to 2022, was performed.

RESULTS

Of the 20 cases, 10 each were seen in men and women. The epicenter of the lesions varied in location: in the maxilla in 8 patients, in the mandible in 5, in the temporal bone in 3, in the sphenoid/clivus in 3, and in the orbit in 1 patient. On the radiographs, the lesions appeared well-circumscribed, expansile, and lytic. On CT, the lesions were predominantly multiloculated, with thin septa, a soft-tissue component, and with expansion and remodeling of the underlying bone. On MR imaging, the solid component of the lesions was isointense on T1WI and hypointense on T2WI, with heterogeneous enhancement of the solid component and rim enhancement of the locules. Fluid-fluid levels were present in 3 patients.

CONCLUSIONS

Giant cell granulomas commonly present as locally aggressive, expansile, multiloculated lytic lesions, with solid as well as cystic areas. The solid component is typically hypointense on T2WI. Certain key imaging features of giant cell granulomas can aid the radiologist in narrowing the differential diagnosis.

Spinal giant cell-rich osteosarcoma-diagnostic dilemma and treatment strategy: A case report

BACKGROUND

Giant cell-rich osteosarcoma (GCRO) is a rare histological variant of osteosarcoma. Spinal GCROs are extremely rare, with challenging diagnosis and management. Herein, we present a case of spinal GCRO at T2, which was not diagnosed in initial biopsy but after T2 corpectomy. We detailed the clinical course, management strategy, and outcome after a 4-year follow-up.

CASE SUMMARY

A 17-year-old female patient presented with back pain followed by ascending paresthesia. Spinal computed tomography (CT) and magnetic resonance imaging (MRI) revealed a collapsed T2 vertebra with an enhancing osteolytic mass. CT-guided biopsy showed inconclusive morphology. Pathology from T2 corpectomy revealed GCRO. The patient subsequently received neoadjuvant chemotherapy followed by salvage operation of T2 costotransversectomy with grossly-total resection adjuvant chemoradiation. Upon treatment completion, she had complete GCRO remission. The 4-year follow-up spinal MRI showed no tumor recurrence.

CONCLUSION

Spinal GCRO poses unique challenges in obtaining sufficient tissue diagnosis and complete surgical removal. However, long-term local control of spinal GCRO is possible following complete resection and adjuvant chemoradiation

Anti-histone H3.3K36M Antibody is a Highly Sensitive and Specific Immunohistochemistry Marker for the Diagnosis of Chondroblastoma. A Validation Based on Study 136 Cases Comprising Chondroblastoma and its Mimics from Single a Centre in India

Introduction: Chondroblastoma has a wide range of differential diagnosis encompassing various benign and malignant entities. The closest differential diagnosis is giant cell tumor of the bone due to overlapping radiological and histomorphological features. Extensive aneurysmal bone cyst like changes and lack of adequately sampled chondroid matrix often masquerades the primary bone lesion and amplifies the diagnostic difficulty in small biopsies with limited tissue. Immunohistochemistry is helpful in such instances to resolve the diagnostic dilemma. Objectives: To analyze the immunohistochemical expression of anti-histone H3F3K36M antibody inchondroblastoma and validate its utility in differentiating chondroblastomafrom its histological mimics. Material and methods: Immunohistochemistry was performed using anti-histone antibody H3.3K36M in 44 histologically diagnosed chondroblastoma and 92 other histological mimickers. All chondroblastoma and giant cell tumor of the bone included in the study were also tested for anti-histone H3.3 G34W antibody. Of the 33 giant cell tumors of bone with classic morphology and imaging findings, 24 H3.3 G34W positive and 9 negative tumors were included intentionally to rule out the possibility of chondroblastoma. The sensitivity, specificity, positive and negative predictive value of marker with regard to chondroblastoma was calculated. Results: Immunohistochemistry revealed unequivocal nuclear positivity for H3.3K36M in the mononuclear cells in all the 44 Chondroblastoma tested, denoting a sensitivity of 100% cases. Allthesetumors tested simultaneously for anti-histone H3.3G34W were negative. None of the histological mimickers were positive H3.3K36M indicating a specificity of 100%. The positive and negative predictive value was 100%. Conclusion: H3.3K36M mutant antibody is highly sensitive and specific IHC marker and can be used as a valuable adjunct to distinguish chondroblastomafrom its histological mimics especially on small biopsies.

Secondary Malignancy in Giant Cell Tumor: A Single-Center Study

Giant cell tumor of bone (GCTB) undergoes a sarcomatous transformation. Secondary malignancy in giant cell tumor (MGCT) is associated with radiotherapy and has a dismal prognosis. We reviewed medical records to investigate the clinicopathological characteristics and prognosis of MGCT patients. The enrollment criterion was high-grade spindle-cell sarcoma, which developed at the site of prior GCTB treatment. Twelve patients were analyzed: six females and six males. The median age was 42.5 years. Benign recurrence occurred in five GCTB patients not treated with radiotherapy. No pulmonary implants were observed. The median latency to the malignant transformation was 63 months. Nine patients were AJCC stage IIB, and three were stage IVA. The median follow-up period after malignant transformation was 62.5 months. Five patients developed local recurrence, and six had distant metastasis. Five-year overall recurrence and metastasis-free survival rates were 61.9%, 66.7%, and 58.3%, respectively. Initial metastasis was a predictive factor for overall survival. Benign local recurrence of GCTB was also a negative factor for metastasis-free survival of MGCT patients. Differences in overall survival according to benign recurrence also showed a tendency toward significance. In our series, secondary MGCT did not occur after radiotherapy. The prognosis was better than previous findings. Benign recurrence of GCTB could reflect the prognosis of MGCT.

Establishment and characterization of NCC-GCTB5-C1: a novel cell line of giant cell tumor of bone

Giant cell tumor of bone (GCTB), is a rare intermediate malignant bone tumor with high local infiltrative ability, and is genetically characterized by mutation in the H3-3A gene. Standard treatment is curative surgical tumor resection. GCTB demonstrates both local recurrence and pulmonary metastasis after surgical treatment, and effective systematic chemotherapy is yet to be established. Therefore, development of novel chemotherapies for GCTB is necessary. Although patient-derived tumor cell lines are potent tools for preclinical research, 15 GCTB cell lines have been reported to date, and only four are publicly available. Thus, this study aimed to establish and characterize a novel GCTB cell line for preclinical studies on GCTB. Herein, we described the establishment of a cell line, NCC-GCTB5-C1, from the primary tumor tissue of a patient with GCTB. NCC-GCTB5-C1 was shown to harbor a mutation in the H3-3A gene, which is typical of GCTB; thus, it has useful properties for in vitro studies. We conducted the largest integrated screening analysis of 214 antitumor agents using NCC-GCTB5-C1 along with four GCTB cell lines. Romidepsin (a histone deacetylase inhibitor), camptothecin, and actinomycin D (topoisomerase inhibitors) demonstrated remarkable antitumor effects, suggesting that these antitumor agents are potential therapeutic candidates for GCTB treatment. Therefore, the NCC-GCTB5-C1 cell line could potentially contribute to the elucidation of GCTB pathogenesis and the development of novel GCTB treatments.

Epigenetic lockdown of CDKN1A (p21) and CDKN2A (p16) characterises the neoplastic spindle cell component of giant cell tumours of bone

Giant cell tumour of bone (GCTB) comprises the eponymous osteoclastic multinucleated giant cells eliciting bone lysis, a H3F3A-mutated neoplastic mononucleated fibroblast-like cell population and H3F3A-wild type mononucleated stromal cells. In this study, we characterised four new cell lines from GCTB. Furthermore, we compared the genome-wide DNA methylation profile of 13 such tumours and three further cell lines with giant cell rich lesions comprising three H3F3B-mutated chondroblastomas, three USP6-rearranged aneurysmal bone cysts, three non-ossifying fibromas, two hyperparathyroidism-associated brown tumours as well as mesenchymal stem cells, osteoblasts, and osteoclasts. In an unsupervised analysis, we delineated GCTB and chondroblastomas from the other analysed tumour entities. Using comparative methylation analysis, we demonstrated that the methylation pattern of the cell lines approximately equals that of H3F3A-mutated stromal cells in tissue. These patterns more resemble that of osteoblasts than that of mesenchymal stem cells, which argues for the osteoblast as the cell of origin of giant cell tumours of bone. Using enrichment analysis, we detected distinct hypermethylated clusters containing histone and collagen genes as well as target genes of the tumour suppressor p53. We found that the promotor regions of CDKN1A, CDKN2A and IGFBP3 are methylated more strongly in GCTB than in the other giant cell containing lesions, mesenchymal stem cells, osteoblasts, and osteoclasts (p<0.001). This hypermethylation correlates with the lower gene expression at the mRNA level for these three genes in the cell lines, the lack of p16 and p21 in these cell lines and the lower expression of p16 and p21 in GCTB. Overall, our analysis reveals characteristic DNA methylation patterns of giant cell tumours of bone and chondroblastomas and shows that cell lines of giant cell tumours of bone are a valid model for further analysis of H3F3A-mutated tumour cells. This article is protected by copyright. All rights reserved.

[Giant-cell tumor of bone in 2022]

Giant cell tumors of bone (GCTs) are rare mesenchymal tumors classified as intermediate in the WHO 2020 classification, i.e. neither completely benign nor definitely malignant, due to recurrence (frequent) and pulmonary metastases (rare). They involve the end of long bones as well as the axial bones of mature skeletons. They are made of mononuclear stromal tumor cells of (pre-) osteoblastic phenotype, mononuclear cells of the monocyte-macrophage lineage and osteoclast-like multinuclear giant cells responsible for tumor osteolysis. In 95% of cases, the stromal cells have a specific mutation in the H3F3A gene which encodes histone H3.3. The mutated H3.3 G34W protein (90% of cases) can be easily detected by immunohistochemistry, even on small samples. Many tumors or bone pseudotumors contain osteoclast-like giant cells, cells of the bone microenvironment, and should not be confused with GCT: mainly brown tumor of hyperparathyroidism, aneurysmal bone cyst, chondroblastoma, non-ossifying fibroma and central giant cell granuloma.

Histological and immunohistochemical features and genetic alterations in the malignant progression of giant cell tumor of bone: a possible association with TP53 mutation and loss of H3K27 trimethylation

In rare cases, giant cell tumor of bone (GCTB) can undergo primary or secondary malignant transformation to malignant giant cell tumor of bone (MGCTB), but the details of the molecular alterations are still unclear. The present study aimed to elucidate the clinicopathologic and molecular features of MGCTBs based on immunohistochemistry, fluorescence in situ hybridization (FISH) and next generation sequencing (NGS) of nine MGCTBs (five primary and four secondary). Seven (78%) of 9 MGCTBs were immunohistochemically positive for H3.3 G34W. In two (22%) patients, although GCTB components were focally or diffusely positive for H3.3 G34W, their malignant components were entirely negative for H3.3 G34W, which was associated with heterozygous loss of H3F3A by FISH. NGS on four MGCTBs revealed pathogenic mutations in TP53 (n = 3), EZH2 (n = 1) and several other genes. Immunohistochemical analysis of the nine MGCTBs confirmed the p53 nuclear accumulation (n = 5) and loss of H3K27me3 expression (n = 3) and showed that they were mutually exclusive. In addition, four (80%) of five cases of pleomorphic or epithelioid cell-predominant MGCTBs were positive for p53, while three (75%) of four cases of spindle cell-predominant MGCTBs were negative for trimethylation at lysine 27 of histone 3 (H3K27me3). The results suggested that p53 alteration and dysfunction of histone methylation as evidenced by H3K27me3 loss may play an important role in the malignant progression of GCTB, and might contribute to the phenotype-genotype correlation in MGCTB. The combined histologic, immunohistochemical and molecular information may be helpful in part for the diagnosis of challenging cases.

Malignant giant cell tumour of bone: a review of clinical, pathological and imaging features

Giant cell tu mour accounts for up to 5% of all bone tumours and malignant giant cell tumour arises in < 10% of cases, representing sarcomatous transformation. Primary malignant giant cell tumour of bone occurs when sarcomatous tissue is observed within conventional giant cell tumour histologically on initial presentation. Secondary malignant giant cell tumour of bone occurs in a region of previously treated giant cell tumour, with most cases arising due to prior radiotherapy. Malignancy in giant cell tumour of bone does not have any unique clinical or imaging features compared to conventional aggressive disease. Historically, malignant giant cell tumour of bone has a poor prognosis which is worse in cases of secondary malignancy. This article aims to present the clinical, pathological and imaging features of MGCTB based on a review of the literature and illustrated by examples from our experience.

Recurrent Fusion of the Genes for High-mobility Group AT-hook 2 (HMGA2) and Nuclear Receptor Co-repressor 2 (NCOR2) in Osteoclastic Giant Cell-rich Tumors of Bone

BACKGROUND/AIM

Chimeras involving the high-mobility group AT-hook 2 gene (HMGA2 in 12q14.3) have been found in lipomas and other benign mesenchymal tumors. We report here a fusion of HMGA2 with the nuclear receptor co-repressor 2 gene (NCOR2 in 12q24.31) repeatedly found in tumors of bone and the first cytogenetic investigation of this fusion.

MATERIALS AND METHODS

Six osteoclastic giant cell-rich tumors were investigated using G-banding, RNA sequencing, reverse transcription polymerase chain reaction, Sanger sequencing, and fluorescence in situ hybridization.

RESULTS

Four tumors had structural chromosomal aberrations of 12q. The pathogenic variant c.103_104GG>AT (p.Gly35Met) in the H3.3 histone A gene was found in a tumor without 12q aberration. In-frame HMGA2-NCOR2 fusion transcripts were found in all tumors. In two cases, the presence of an HMGA2-NCOR2 fusion gene was confirmed by FISH on metaphase spreads.

CONCLUSION

Our results demonstrate that a subset of osteoclastic giant cell-rich tumors of bone are characterized by an HMGA2-NCOR2 fusion gene.

Diagnostic Utility of Genetic and Immunohistochemical H3-3A Mutation Analysis in Giant Cell Tumour of Bone

To validate the reliability and implementation of an objective diagnostic method for giant cell tumour of bone (GCTB). H3-3A gene mutation testing was performed using two different methods, Sanger sequencing and immunohistochemical (IHC) assays. A total of 214 patients, including 120 with GCTB and 94 with other giant cell-rich bone lesions, participated in the study. Sanger sequencing and IHC with anti-histone H3.3 G34W and G34V antibodies were performed on formalin-fixed, paraffin-embedded tissues, which were previously decalcified in EDTA if needed. The sensitivity and specificity of the molecular method was 100% (95% CI: 96.97–100%) and 100% (95% CI: 96.15–100%), respectively. The sensitivity and specificity of IHC was 94.32% (95% CI: 87.24–98.13%) and 100% (95% CI: 93.94–100.0%), respectively. P.G35 mutations were discovered in 2/9 (22.2%) secondary malignant GCTBs and 9/13 (69.2%) GCTB after denosumab treatment. We confirmed in a large series of patients that evaluation of H3-3A mutational status using direct sequencing is a reliable tool for diagnosing GCTB, and it should be incorporated into the diagnostic algorithm. Additionally, we discovered IHC can be used as a screening tool. Proper tissue processing and decalcification are necessary. The presence of the H3-3A mutation did not exclude malignant GCTB. Denosumab did not eradicate the neoplastic cell population of GCTB.

Clinical and pathological analysis of giant cell tumor of bone with denosumab treatment and local recurrence

BACKGROUND

Giant cell tumor of bone (GCTB) is a primary bone tumor which comprises giant cells and two types of stromal cells. Recent studies have suggested therapeutic risks of denosumab. No previous studies have reported changes in serum TRACP-5b and SUVmax of ¹⁸F-FDG-PET/CT in recurred GCTB after denosumab treatment. Therefore, we assessed the relationship between clinical and pathological features of GCTB which recurred after denosumab treatment.

METHODS

We retrospectively reviewed the medical records of 26 patients with GCTB who underwent curettage between 2010 and 2018. Fourteen patients treated with denosumab were defined as the denosumab group. We evaluated TRACP-5b and SUVmax values in the denosumab group. H&E staining and immunohistochemistry for H3.3 G34W were performed for pathological assessment. Twelve patients treated without denosumab were defined as the non-denosumab group and compared with denosumab group.

RESULTS

The local recurrence rate in the denosumab group was 57.4%. The mean TRACP-5b and SUVmax values were significantly decreased after denosumab therapy (P < 0.001, 1077 ± 161 to 74 ± 9 mU/dL and 8.88 ± 0.40 to 3.79 ± 0.56, respectively). Both parameters significantly increased with local recurrence. H&E staining after denosumab treatment revealed the disappearance of giant cells and histological changes in stromal cells. Specimens of local recurrence subjected to H&E staining and immunohistochemistry for H3.3 G34W demonstrated almost identical features to those in the first biopsy.

CONCLUSION

Although denosumab can prevent GCTB from osteolysis, local recurrence cannot be reduced by denosumab treatment. The clinical and pathological results were almost the same as those before denosumab treatment, suggesting that the changes of GCTB by denosumab are reversible.

Giant Cell-Rich Tumors of Bone

The term giant cell-rich tumors of bone refers to a shared morphologic pattern in a group of different osseous lesions, that is, the abundance of osteoclastlike giant cells. Fitting with a broad spectrum of clinical presentations and biological behavior, the recent detection of characteristic molecular alterations in giant cell tumor of bone (H3-3), nonossifying fibroma (KRAS, FGFR1), giant cell granuloma of the jaws (KRAS, FGFR1, TRPV4), and aneurysmal bone cyst (USP6) have contributed significantly to the biological understanding of these morphologically related but clinically distinct lesions and their systematic classification, highlighting differences and pathogenic relationships.

Establishment and characterization of the NCC-GCTB4-C1 cell line: a novel patient-derived cell line from giant cell tumor of bone

Giant cell tumor of bone (GCTB) is a rare osteolytic intermediate bone tumor that harbors a pathogenic H3F3A gene mutation and exhibits characteristic histology. The standard curative treatment for GCTB is complete surgical resection, but it frequently results in local recurrence and, more rarely, metastasis. Therefore, effective multidisciplinary treatment is needed. Although patient-derived tumor cell lines are promising tools for preclinical and basic research, there are only four available cell lines for GCTB in public cell banks. Thus, the aim of this study was to establish a novel GCTB cell line. Using surgically resected tumor tissues from a patient with GCTB, we established a cell line named NCC-GCTB4-C1. The cells harbored the typical H3F3A gene mutation and exhibited constant proliferation and invasive capabilities. After characterizing NCC-GCTB4-C1 cell behaviors, we conducted high-throughput screening of 214 anti-tumor drugs and identified seven effective drugs. Comparing the results of high-throughput screening using NCC-GCTB4-C1 cell line with the results using NCC-GCTB1-C1, NCC-GCTB2-C1, and NCC-GCTB3-C1 cell lines that we previously established, four drugs were in common effective. This study showed potential drugs for the treatment of GCTB. These data indicate that NCC-GCTB4-C1 has the potential to be a powerful tool in preclinical and basic research on GCTB.

Spontaneous Regression of Brown Tumor in a Patient Treated With Peritoneal Dialysis

A 52-year-old man, with a history of diabetic nephropathy and renal cancer, had been treated with peritoneal dialysis for four months before consulting our hospital. At the time of imaging evaluation, three years after surgery for renal cancer, fluorodeoxyglucose accumulation was found at the distal metaphysis of the left radius. After the biopsy, he was diagnosed with giant cell tumor of bone (GCTB), and surgery was scheduled. However, osteogenesis was observed in the images retaken before surgery. It was found that his intact parathyroid hormone level had been abnormally high four months prior to his visit to us but had subsequently normalized. The tissue obtained by re-biopsy revealed osteogenesis with the disappearance of multinucleated giant cells, suggesting a brown tumor (BT). The tumor was thought to have been caused by secondary hyperparathyroidism (HPT) associated with peritoneal dialysis. When osteolytic lesions mimicking GCTB are found, the possibility of BT should be considered based on comorbidities and clinical information.

Reliability and Role of Mutation-specific H3F3A (Histone 3-3) G34W Immunohistochemistry to Differentiate Giant Cell Tumor of Bone From its Clinicoradiologic and Histologic Mimics: An Institutional Study

Giant cell tumor of bone (GCTB) is a benign neoplasm, which can sometimes be a diagnostic challenge, especially in small biopsies, due to its histologic benign and malignant mimics. We evaluated the role of H3.3 G34W immunohistochemistry (IHC) antibody in diagnosing GCTB and its role in differentiating it from its close histologic mimics. A total of 120 cases (80 cases of GCTB and 40 cases of histologic mimics) were retrieved and subjected to IHC. Of 80 cases of GCTB, 72 cases showed a positive nuclear immunoexpression, while all 40 cases of histologic mimics of GCTB showed a negative staining for H3.3 G34W IHC. Sensitivity and specificity of this mutation-specific antibody for diagnosis of GCTB was 90% and 100%, respectively, while, the positive predictive value and the negative predictive value were 100% and 83.3%, respectively. A positive expression of H3.3 G34W was seen in all 5 cases of GCTB, postdenosumab therapy, as well as, in all 3 cases of malignant giant cell tumor. The presented study showed that H3.3 G34W mutation-specific IHC is a reliable and specific marker for GCTB and can help distinguish it from the histologic mimics due to distinct therapeutic implications.

Multiple versus solitary giant cell lesions of the jaw: Similar or distinct entities?

The majority of giant cell lesions of the jaw present as a solitary focus of disease in bones of the maxillofacial skeleton. Less frequently they occur as multifocal lesions. This raises the clinical dilemma if these should be considered distinct entities and therefore each need a specific therapeutic approach. Solitary giant cell lesions of the jaw present with a great diversity of symptoms. Recent molecular analysis revealed that these are associated with somatic gain-of-function mutations in KRAS, FGFR1 or TRPV4 in a large component of the mononuclear stromal cells which all act on the RAS/MAPK pathway. For multifocal lesions, a small group of neoplastic multifocal giant cell lesions of the jaw remain after ruling out hyperparathyroidism. Strikingly, most of these patients are diagnosed with jaw lesions before the age of 20 years, thus before the completion of dental and jaw development. These multifocal lesions are often accompanied by a diagnosis or strong clinical suspicion of a syndrome. Many of the frequently reported syndromes belong to the so-called RASopathies, with germline or mosaic mutations leading to downstream upregulation of the RAS/MAPK pathway. The other frequently reported syndrome is cherubism, with gain-of-function mutations in the SH3BP2 gene leading through assumed and unknown signaling to an autoinflammatory bone disorder with hyperactive osteoclasts and defective osteoblastogenesis. Based on this extensive literature review, a RAS/MAPK pathway activation is hypothesized in all giant cell lesions of the jaw. The different interaction between and contribution of deregulated signaling in individual cell lineages and crosstalk with other pathways among the different germline- and non-germline-based alterations causing giant cell lesions of the jaw can be explanatory for the characteristic clinical features. As such, this might also aid in the understanding of the age-dependent symptomatology of syndrome associated giant cell lesions of the jaw; hopefully guiding ideal timing when installing treatment strategies in the future.

Angiogenesis pattern and H3.3 histone mutation in aggressive and non-aggressive central giant cell lesions

OBJECTIVE

The aim of this study was to evaluate angiogenesis in central giant cell lesions (CGCL) and its association with biological behavior. In addition, investigation of the histone H3.3 mutation was performed.

DESIGN

Thirty-eight cases of CGCL were classified as aggressive (n = 9) or nonaggressive (n = 29). Cases were submitted to immunohistochemistry to compare angiogenesis using Wilms' tumor protein 1 (WT1), platelet endothelial cell adhesion molecule (CD31) and endoglin (CD105) between groups. To verify the presence of genic mutation, histone H3.3 was investigated.

RESULTS

WT1 was expressed in mononuclear and giant cells of all cases. CD31 and CD105 were expressed in CGCL microvessels, with a higher CD105 microvascular density than CD31. No statistically significant difference was observed between groups. None of the cases studied showed the histone mutation.

CONCLUSIONS

There was no difference between aggressive and nonaggressive lesions regarding the angiogenic markers. The expression of WT1 and CD105 suggests that CGCL presents a tumoral vascular pattern with high neoangiogenic activity. The absence of histone mutation may indicate that CGCL is not a true giant cell tumor.

Establishment and characterization of novel patient-derived cell lines from giant cell tumor of bone

Giant cell tumor of bone (GCTB) is a locally aggressive and rarely metastasizing tumor. GCTB is characterized by the presence of unique giant cells and a recurrent mutation in the histone tail of the histone variant H3.3, which is encoded by H3F3A on chromosome 1. GCTB accounts for ~ 5% of primary bone tumors. Although GCTB exhibits an indolent course, it has the potential to develop aggressive behaviors associated with local recurrence and distant metastasis. Currently, complete surgical resection is the only curative treatment, and novel therapeutic strategies are required. Patient-derived cancer cell lines are critical tools for basic and pre-clinical research. However, only a few GCTB cell lines have been reported, and none of them are available from public cell banks. Therefore, we aimed to establish novel GCTB cell lines in the present study. Using curetted tumor tissues of GCTB, we established two cell lines and named them NCC-GCTB2-C1 and NCC-GCTB3-C1. These cells harbored a typical mutation in histones and exhibited slow but constant growth, formed spheroids, and had invasive capabilities. We demonstrated the utility of these cell lines for high-throughput drug screening using 214 anticancer agents. We concluded that NCC-GCTB2-C1 and NCC-GCTB3-C1 cell lines were useful for the in vitro study of GCTB.

Tumor microenvironment in giant cell tumor of bone: evaluation of PD-L1 expression and SIRPα infiltration after denosumab treatment

Giant cell tumor of bone (GCTB) is an intermediate malignant bone tumor that is locally aggressive and rarely metastasizes. Denosumab, which is a receptor activator of nuclear factor kappa B ligand (RANKL) inhibitor, can be used to treat GCTB. We focused on potential immunotherapy for GCTB and investigated the tumor microenvironment of GCTB. Programmed death-ligand 1 (PD-L1) and indoleamine 2,3-dioxygenase 1 (IDO1) expression and signal-regulatory protein alpha (SIRPα), forkhead box P3 (FOXP3), and cluster of differentiation 8 (CD8) infiltration were assessed by immunohistochemical studies of 137 tumor tissues from 96 patients. Of the naive primary specimens, 28% exhibited PD-L1 expression and 39% exhibited IDO1 expression. There was significantly more SIRPα⁺, FOXP3⁺, and CD8⁺ cell infiltration in PD-L1- and IDO1-positive tumors than in PD-L1- and IDO1-negative tumors. The frequency of PD-L1 expression and SIRPα⁺ cell infiltration in recurrent lesions treated with denosumab was significantly higher than in primary lesions and recurrent lesions not treated with denosumab. PD-L1 expression and higher SIRPα⁺ cell infiltration were significantly correlated with shorter recurrence-free survival. PD-L1 and SIRPα immune checkpoint inhibitors may provide clinical benefit in GCTB patients with recurrent lesions after denosumab therapy.

Neurofibromatosis Type 1 With Cherubism-like Phenotype, Multiple Osteolytic Bone Lesions of Lower Extremities, and Alagille-syndrome: Case Report With Literature Survey

BACKGROUND/AIM

Neurofibromatosis type 1 (NF) is an autosomal dominant hereditary disease. The cardinal clinical findings include characteristic skeletal alterations. Difficulties in diagnosis and therapy can arise if an individual has further illnesses.

CASE REPORT

This is a case report of a 16-year-old patient affected by NF1. She also suffered from Alagille syndrome and the consequences of fetal alcohol exposure. The patient's facial phenotype showed findings that could be assigned to one or more of the known diseases. The patient was referred for treating a cherubism-like recurrent central giant cell granuloma (CGCG) of the jaw. The patient developed bilateral, multilocular non-ossifying fibromas (NOF) of the long bones of the lower extremity. Treatment of the skeletal lesions consisted of local curettage. While NOF regressed after surgery, the CGCG of the jaw remained largely unchanged. Extensive genetic tests confirmed a previously unknown germline mutation in the JAG1 gene, the germline mutation of the NF1 gene, and the somatic mutation in the NF1 gene in the diffuse plexiform neurofibroma, but not in the CGCG.

CONCLUSION

Assigning facial findings to a defined syndrome is ambiguous in many cases and especially difficult in patients who have multiple diseases that can affect the facial phenotype. Surgical therapy should be adapted to the individual findings.

A common classification framework for histone sequence alterations in tumours: an expert consensus proposal

The description of genetic alterations in tumours is of increasing importance. In human genetics, and in pathology reports, sequence alterations are given using the human genome variation society (HGVS) guidelines for the description of such variants. However, there is less adherence to these guidelines for sequence variations in histone genes. Due to early cleavage of the N-terminal methionine in most histones, the description of histone sequence alterations follows their own nomenclature and differs from the HGVS-compliant numbering by omitting this first amino acid. Next generation sequencing reports, however, follow the HGVS guidelines and as a result, an unambiguous description of sequence variants in histones cannot be provided. The coexistence of these two nomenclatures leads to confusions for pathologists, oncologists, and researchers. This review provides an overview of tumour entities with sequence alterations of the H3-3A gene (HGNC ID = HGNC:4764), highlights the problems associated with the coexistence of these two nomenclatures, and proposes a standard for the reporting of histone sequence variants that allows an unambiguous description of these variants according to HGVS principles. We hope that scientific journals will adopt the new notation, and that both geneticists and pathologists will include it in their reports. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.