Diagnostic utility of histone H3.3 G34W, G34R, and G34V mutant-specific antibodies for giant cell tumors of bone

Establishment of patient-derived 3D in vitro models of sarcomas: literature review and guidelines on behalf of the FORTRESS working group

Sarcomas are a large family of rare and heterogeneous mesenchymal tumors, which respond poorly to available systemic treatments. Translation of preclinical findings into clinical applications has been slow, limiting improvements in patients' outcomes and ultimately highlighting the need for a better understanding of sarcoma biology to develop more effective, subtype-specific therapies. To this end, reliable preclinical models are crucial, but the development of 3D in vitro sarcoma models has been lagging behind that of epithelial cancers. This is primarily due to the rarity and heterogeneity of sarcomas, and lack of widespread knowledge regarding the optimal growth conditions of these in vitro models. In this review, we provide an overview of currently available sarcoma tumoroid models, together with guidelines and suggestions for model development and characterization, on behalf of the FORTRESS (Forum For Translational Research in Sarcomas) international research working group on 3D sarcoma models.

Update on the nature of central giant cell granuloma of the jaw with a focus on the aggressive subtype

Central giant cell granuloma (CGCG) is a benign, localised osteolytic lesion of the jaw ​that is categorised into non-aggressive and aggressive subtypes. In contrast to non-aggressive CGCG, aggressive CGCG is characterised by pain, paraesthesia, root resorption, rapid growth, a size of >5 cm, cortical perforation, or recurrence after surgical treatment. However, the nature of CGCG, especially aggressive CGCG, remains unclear. This study was performed to analyse the systematic and comprehensive characteristics of CGCG of the jaw, especially the aggressive subtype, and first explored the genetic variation of aggressive CGCG by whole-exome sequencing. In total, 42 CGCGs were analysed (including 25 non-aggressive and 17 aggressive subtypes). H3F3A mutations were not detected in these CGCGs through immunohistochemistry and Sanger sequencing. The inability to detect H3F3A mutations could help differentiate CGCG from giant cell tumour of bone, indicating the two diseases are not different stages of the same pathological entity. Additionally, fluorescence in situ hybridisation did not reveal USP6 gene rearrangement in CGCG, which could distinguish it from aneurysmal bone cysts, especially the solid type. Therefore, H3F3A mutation and USP6 gene rearrangement detection have great significance in the clinicopathological diagnosis of CGCG of the jaw in terms of their ability to exclude giant cell tumour of bone and aneurysmal bone cyst. Moreover, the whole-exome sequencing data indicated that LRP1B gene abnormalities might be related to the aggressive biological behaviour of CGCG, and that NOTCH4 mutation could be a novel therapeutic target for aggressive CGCG.

Surgical and radiological outcomes of giant cell tumor of the bone: prognostic value of Campanacci grading and selective use of denosumab

BACKGROUND

Advancements in diagnostic and therapeutic modalities for giant cell tumors of bone (GCTB) have introduced molecular and radiological tools that refine clinical decision-making. H3.3 G34W immunohistochemical staining has become a routine diagnostic marker, while H3F3A mutational analysis enhances prognostic insights. Treatment primarily involves surgical methods such as curettage or en bloc resection, with denosumab serving as an adjunct in high-risk or inoperable cases.

METHODS

We retrospectively analyzed 55 patients with GCTB, focusing on clinicopathologic and radiological findings. Tumors were evaluated using the Campanacci grading system. Immunohistochemical analysis with H3.3 G34W antibody and next-generation sequencing (NGS) were performed to detect H3F3A mutations. A subgroup of nine patients treated with denosumab was further analyzed for clinical outcomes and histological changes.

RESULTS

The cohort had a mean age of 37.7 years, with tumors most commonly affecting the knee joint (55%). All tested tumors demonstrated positive H3.3 G34W staining, with eight exhibiting H3F3A G34W mutations. Recurrence rates were 32% following curettage and 18% after en bloc resection. Denosumab treatment, administered for an average of 14.6 months, facilitated tumor downsizing and new bone formation without major side effects. Histologically, treated tumors showed a depletion of giant cells and increased bone matrix deposition.

CONCLUSIONS

Surgery remains the cornerstone of GCTB treatment, with curettage or resection tailored to tumor characteristics. Denosumab offers a valuable adjunct in high-risk cases, enhancing surgical feasibility and promoting joint preservation. The Campanacci grading system continues to be a crucial tool for prognostication and treatment planning, particularly when complemented by molecular and radiological diagnostics. Future research should focus on integrating advanced imaging and artificial intelligence for personalized GCTB management.

LEVEL OF EVIDENCE

Level 4.

Role of H3F3A (H3G34W) antibody in the diagnosis of giant cell tumour of bone in the paediatric age group

Giant cell tumour of the bone (GCTB) occurring in paediatric patients is rare and may presents with atypical histology. Given that giant cell tumour mimics, such as osteosarcoma, are more prevalent in this demographic, diagnosing GCTB can often be challenging. This study aimed to investigate the efficacy of H3F3A immunohistochemistry (IHC) in the diagnosis of GCTB in the immature skeleton. This retrospective study included paediatric patients who were diagnosed with GCTB between 2009 and 2024. Histological features were re-evaluated and IHC staining was performed. Giant cell tumour mimics were included in the control group. 72 biopsy proven GCTB were reported in the paediatric patients during the study period. The age ranged from 12 to 18 years, with a median age of 16 ( ± 1.8) years. 49 (68.1 %) were females and 23 (31.9 %) were males (female to male ratio of 2.1:1). Tibia was most common site (23) involved followed by femur (12), fibula (8) and small bones of hand and feet (8). H3G34W was positive in 61 (84.7 %) of GCTB cases (p < 0.01); and negative in all 33 GCTB mimics. H3G34V was positive in 3 of 11 H3G34W negative cases. All these 11 cases were negative for H3G34R and keratin AE1/AE3. Significant association of GCTB was found with gender (p = 0.02) and site of the tumour (p < 0.01). HG34W was not associated with tumour site (p = 0.4533) or biopsy yield (p = 0.4533). A sensitivity of 84.74 %, specificity of 100 %, positive predictive value of 75 % and negative predictive value of 100 % was established. An ROC was constructed, with area under the curve of 0.924 (95 % CI 0.88-0.97). In conclusion H3G34W antibody is a valuable diagnostic tool for accurately diagnosing GCTB and distinguishing it from other giant cell mimics. Additionally, since a minimal tissue yield is adequate for determining the diagnosis, the need for larger biopsies is reduced.

Role of epigenetics in paediatric cancer pathogenesis & drug resistance

Paediatric oncogenesis is tightly intertwined with errors in developmental processes involving cell specification and differentiation, which are governed by intricate temporal epigenetic signals. As paediatric cancers are characterised by a low number of somatic mutations, dysregulated chromatin landscapes are believed to be key drivers of oncogenesis. Epigenetic dysregulation is induced by mutations and aberrant expression of histones and epigenetic regulatory genes, to altered DNA methylation patterns and dysregulated noncoding RNA expression. In this review, we discuss epigenetic alterations in paediatric cancer oncogenesis and recurrence, and their potential as diagnostic biomarkers. We also discuss various epigenetic drugs that have entered clinical trials for aggressive paediatric cancers. Targeting paediatric-specific epigenetic vulnerabilities may improve recurrence-free survival in high-risk cancers.

Recent topics in diagnosis and treatment of malignant spinal tumors

The diagnosis and treatment of malignant spinal tumors are complex and require an integrated approach known as Jaffe's triangle.　This review discusses recent topics in the diagnosis and treatment of primary and metastatic malignant spinal tumors.　Integrated diagnostic methods, including the development of a dumbbell scoring system for benign-malignant differentiation and the use of positron emission tomography and magnetic resonance imaging (PET-MRI), have improved diagnostic accuracy.　Curative resection techniques such as vertebrectomy, sagittal resection, and posterior resection are crucial for primary malignant tumors.　Heavy particle radiation therapy, such as carbon-ion radiotherapy, shows promise against radiation-resistant tumors, whereas novel drug therapies, such as denosumab, are effective for giant cell tumors of the bone arising in the spine.　For metastatic spinal tumors, the collaborative efforts of the Bone Metastasis Cancer Board and minimally invasive spine stabilization have expanded surgical indications and improved patient outcomes.　The treatment system has shifted towards preventive surgery and outpatient management, aiming to maintain quality of life and continue chemotherapy.　Interdisciplinary collaboration is essential for improving treatment outcomes in both primary and metastatic malignant spinal tumors.Primary malignant spinal cord tumors (PMST) and metastatic spinal tumors (MST) are among the most difficult areas of orthopedic surgery.　Their diagnosis and treatment require multidisciplinary diagnostic and therapeutic strategies that integrate knowledge and skills in orthopedics, pathology, and diagnostic radiology (the so-called Jaffe triangle), as well as in clinical oncology and tumor biology, which have made remarkable progress in recent years.　Here, we review recent topics related to the diagnosis and treatment of PMST and MST.

Methylation Analysis Reveals Epigenetic Congruence Between Bone Sarcomas With H3-3A Mutations and Malignant Giant Cell Tumors of Bone

Hotspot mutations in H3-3A gene are key drivers in giant cell tumor of bone (GCTB). Rare primary bone sarcomas also harbor this mutation, but their clinicopathologic characteristics and molecular profiles, as well as their relationship to conventional and malignant GCTB (MGCTB) and high-grade conventional osteosarcoma (HGOS), are largely undefined. Herein, we present a series of 10 H3-3A mutated bone sarcomas (BSH3-3A) with a comparative clinicopathologic, mutational, and epigenetic analysis with conventional GCTB, MGCTB, and HGOS. BSH3-3A comprised of 6 high-grade osteosarcomas, 4 undifferentiated pleomorphic sarcoma of bone and occurred in 7 women and 3 men with a mean age of 46 years (28-74 years). The tumors involved femur (n = 4), talus (n = 2), spine (n = 2), pelvis (n = 1), and 1 unknown site. Epiphysis involvement was noted in 2 femoral tumors. In majority of the cases, BSH3-3A showed cellular proliferation of epithelioid and/or spindle cells, hyperchromatic nuclei, and conspicuous pleomorphism with or without osteoid production. One case exhibited both low- and high-grade osteosarcoma components. The mutational profile of BSH3-3A was different than that of conventional HGOS with significantly less frequent TP53 mutations. The genomic index, which reflects the degree of genomic complexity, was also significantly lower in BSH3-3A compared with HGOS, yet higher than GCTB. DNA methylation analysis revealed that most BSH3-3A and MGCTB cases form a distinct cluster, positioned near but separate from GCTB, and clearly separated from HGOS. Differential methylation analysis revealed that BSH3-3A exhibited the highest degree of similarity to MGCTB in comparison to HGOS and GCTB. Survival analysis showed that outcomes for BSH3-3A do not differ significantly from those observed in HGOS or MGCTB. Finally, BSH3-3A tumors, although radiologically and histologically identical to high-grade bone sarcomas lacking H3-3A mutations, display epigenetic features similar to MGCTB and have a significantly less complex genomic profile than HGOS, despite comparable clinical outcomes.

Roles of osteoclasts in pathological conditions

Bone is a unique organ crucial for locomotion, mineral metabolism, and hematopoiesis. It maintains homeostasis through a balance between bone formation by osteoblasts and bone resorption by osteoclasts, which is regulated by the basic multicellular unit (BMU). Abnormal bone metabolism arises from an imbalance in the BMU. Osteoclasts, derived from the monocyte-macrophage lineage, are regulated by the RANKL-RANK-OPG system, which is a key factor in osteoclast differentiation. RANKL activates osteoclasts through its receptor RANK, while OPG acts as a decoy receptor that inhibits RANKL. In trabecular bone, high turnover involves rapid bone formation and resorption, influenced by conditions such as malignancy and inflammatory cytokines that increase RANKL expression. Cortical bone remodeling, regulated by aged osteocytes expressing RANKL, is less understood, despite ongoing research into how Rett syndrome, characterized by MeCP2 abnormalities, affects RANKL expression. Balancing trabecular and cortical bone involves mechanisms that preserve cortical bone, despite overall bone mass reduction due to aging or oxidative stress. Research into genes like sFRP4, which modulates bone mass, highlights the complex regulation by BMUs. The roles of the RANKL-RANK-OPG system extend beyond bone, affecting processes such as aortic valve formation and temperature regulation, which highlight the interconnected nature of biological research.

Pharmacoproteogenomic approach identifies on-target kinase inhibitors for cancer drug repositioning

Drug repositioning of approved drugs offers advantages over de novo drug development for a rare type of cancer. To efficiently identify on-target drugs from clinically successful kinase inhibitors in cancer drug repositioning, drug screening and molecular profiling of cell lines are essential to exclude off-targets. We developed a pharmacoproteogenomic approach to identify on-target kinase inhibitors, combining molecular profiling of genomic features and kinase activity, and drug screening of patient-derived cell lines. This study examined eight patient-derived giant cell tumor of the bone (GCTB) cell lines, all of which harbored a signature mutation of H3-3A but otherwise without recurrent copy number variants and mutations. Kinase activity profiles of 100 tyrosine kinases with a three-dimensional substrate peptide array revealed that nine kinases were highly activated. Pharmacological screening of 60 clinically used kinase inhibitors found that nine drugs directed at 29 kinases strongly suppressed cell viability. We regarded ABL1, EGFR, and LCK as on-target kinases; among the two corresponding on-target kinase inhibitors, osimertinib and ponatinib emerged as on-target drugs whose target kinases were significantly activated. The remaining 26 kinases and seven kinase inhibitors were excluded as off-targets. Our pharmacoproteomic approach enabled the identification of on-target kinase inhibitors that are useful for drug repositioning.

The diagnostic and prognostic value of tartrate-resistant acid phosphatase isoform 5b for giant cell tumor of bone

BACKGROUND

Serum level of tartrate-resistant acid phosphatase 5b (TRACP5b) is an excellent serum marker of bone resorption. In patients with giant cell tumor of bone (GCTB), TRACP5b levels are reportedly elevated. This study investigated whether TRACP5b could be a diagnostic serum marker and be useful for detecting postoperative disease progression for GCTB.

METHODS

Cohort 1: We abstracted data from 120 patients with TRACP5b measurements from our database: 49 patients with GCTB and 71 patients non-GCTB. We compared serum TRACP5b values between the GCTB and non-GCTB groups. Cohort 2 included 47 patients with GCTB who had more than 6 months of follow-up and multiple TRACP5b values. For patients with local recurrence, TRACP5b change rate was calculated by comparing the TRACP5b value just before progression (a) with the value at the time of progression (b): Change rate = [(b)-(a)]/(a). In the non-progression group, the change rate was calculated from the two consecutive TRACP5b values, (c) and (d): Change rate =[(c)-(d)]/(c). We compared TRACP5b change rates between the progression and non-progression groups.

RESULTS

Cohort 1: The GCTB group had a significantly higher mean TRACP5b value (1756 ± 2021 mU/dL) than the non-GCTB group (415 ± 219 mU/dL) (p < 0.0001). Cohort 2: The mean TRACP5b change rate of the progression group was significantly higher than the non-progression group (8.53 ± 8.52 and 0.24 ± 0.27, respectively; p < 0.0001).

CONCLUSION

TRACP5b is a useful diagnostic marker in GCTB. The rate of change in serum TRACP5b values is a highly sensitive marker for predicting local recurrence in GCTB.

The tumor-stroma ratio in giant cell tumor of bone: associations with the immune microenvironment and responsiveness to denosumab treatment

BACKGROUND

Currently, there is limited understanding regarding the clinical significance of the tumor-stroma ratio (TSR) in giant cell tumor of bone (GCTB). Hence, we aimed to investigate the distribution of TSR in GCTB and explore its correlation with various clinicopathologic factors, immune microenvironment, survival prognosis, and denosumab treatment responsiveness.

METHODS

We conducted a multicenter cohort study comprising 426 GCTB patients treated at four centers. TSR was evaluated on hematoxylin and eosin-stained and immunofluorescent sections of tumor specimens. Immunohistochemistry was performed to assess CD3+, CD4+, CD8+, CD20+, PD-1+, PD-L1+, and FoxP3+ TIL subtypes as well as Ki-67 expression levels in 426 tissue specimens. These parameters were then analyzed for their correlations with patient outcomes [local recurrence-free survival (LRFS) and overall survival (OS)], clinicopathological features, and denosumab treatment responsiveness.

RESULTS

Low TSR was significantly associated with poor LRFS and OS in both cohorts. Furthermore, TSR was also correlated with multiple clinicopathological features, TIL subtype expression, and denosumab treatment responsiveness. TSR demonstrated similar predictive capabilities as the conventional Campanacci staging system for predicting patients' LRFS and OS.

CONCLUSION

The results of this study provide evidence supporting the use of TSR as a reliable prognostic tool in GCTB and as a predictor of denosumab treatment responsiveness. These findings may aid in developing individualized treatment strategies for GCTB patients in the future.

Immunohistochemical expression of H3.3 G34W in 100 giant cell tumors of bone and its diagnostic mimics, including its value in resolving uncommon diagnostic scenarios: A single institutional study at a tertiary cancer referral center, India

BACKGROUND

There can be a diagnostic challenge in differentiating giant cell tumor of bone (GCTB) from its mimics. Lately, histone H 3 F 3 A (Histone 3.3 ) G34W has been identified as a promising immunohistochemical marker.

AIMS

This study was aimed at evaluating H3.3 G34W immunostaining in 100 GCTBs, including its value in resolving diagnostic dilemmas.

MATERIALS AND METHODS

Immunohistochemical staining for H3.3 G34W was graded in terms of staining intensity (1+ to 3+) and the percentage of tumor cells showing crisp nuclear staining.

RESULTS

One hundred GCTBs occurred in 58 males and 42 females (M: F ratio = 1.3), of 7-66 years age (average = 31.3, median = 28), commonly in distal femur (26), followed by proximal tibia (17), distal radius (12), proximal humerus (7), metacarpals (7), sacrum (6), proximal fibula (6), and relatively unusual sites (19), including a single multicentric case. Out of 92 GCTBs, wherein H3.3 G34W immunostaining worked, 81 (88.1%) showed positive staining in the mononuclear cells, including tumors with fibrous histiocytoma-like areas, sparing osteoclast-like giant cells, with 3+ staining intensity in 65/81 (80%) tumors. All 7/7 (100%) malignant GCTBs showed positive staining, including the pleomorphic/sarcomatous cells. All 7/7 (100%) metastatic GCTBs showed positive immunostaining. Seven out of 10 post-denosumab treated GCTBs showed positive H3.3 G34W immunostaining in the residual mononuclear cells. None of the other 37 "giant cell-rich" lesions displayed H3.3 G34W immunostaining. Four of 9 GCTBs tested for H3.3 G34W mutation showed positive results.

CONCLUSIONS

The diagnostic sensitivity and specificity of H3.3 G34W for GCTB were 88.1% and 100%, respectively. This constitutes one of the first reports from our country, further validating the diagnostic value of H3.3 G34W in differentiating GCTB, including metastatic and malignant forms from its mimics, including small biopsy samples. Its value in various diagnostic dilemmas is presented and utility in identifying residual tumor cells in post-denosumab treated GCTBs is worth exploring.

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.

Current Concepts in the Treatment of Giant Cell Tumor of Bone: An Update

Curettage is recommended for the treatment of Campanacci stages 1-2 giant cell tumor of bone (GCTB) in the extremities, pelvis, sacrum, and spine, without preoperative denosumab treatment. In the distal femur, bone chips and plate fixation are utilized to reduce damage to the subchondral bone and prevent pathological fracture, respectively. For local recurrence, re-curettage may be utilized when feasible. En bloc resection is an option for very aggressive Campanacci stage 3 GCTB in the extremities, pelvis, sacrum, and spine, combined with 1-3 doses of preoperative denosumab treatment. Denosumab monotherapy once every 3 months is currently the standard strategy for inoperable patients and those with metastatic GCTB. However, in case of tumor growth, a possible malignant transformation should be considered. Zoledronic acid appears to be as effective as denosumab; nevertheless, it is a more cost-effective option. Therefore, zoledronic acid may be an alternative treatment option, particularly in developing countries. Surgery is the mainstay treatment for malignant GCTB.

Immunohistochemistry Update in Dermatopathology and Bone and Soft Tissue Pathology

CONTEXT.—

Immunohistochemistry plays an important role in dermatopathology, particularly for melanocytic lesions and poorly differentiated malignancies. In the field of bone and soft tissue pathology, molecular methods remain the gold standard for diagnosis; however, immunohistochemistry targeting underlying molecular alterations represents a valuable screening tool, especially in areas with limited access to molecular testing.

OBJECTIVE.—

To describe the utility and limitations of new and emerging immunohistochemical stains in the diagnosis of skin, soft tissue, and bone tumors.

DATA SOURCES.—

A literature review of recently described immunohistochemical stains in the fields of dermatopathology and bone and soft tissue pathology was performed.

CONCLUSIONS.—

Immunohistochemistry is an important adjunctive tool for select entities in dermatopathology and bone and soft tissue pathology, and it provides pathologists with valuable evidence of their behavior, underlying molecular alterations, and line of differentiation. Furthermore, immunostains targeting molecular abnormalities have the potential to replace current molecular methods. Many of these recently described stains demonstrate higher sensitivity and specificity; however, limitations and pitfalls still exist, and correlation with morphologic and clinical findings remains essential for diagnosis.

Histological and immunohistochemical analyses of osteoclast maturation in giant cell tumor of bone

INTRODUCTION

Giant cell tumor of bone (GCTB) is a benign but locally aggressive tumor characterized by the occurrence of multinucleated osteoclast-like giant cells that play a key role in GCTB pathogenesis. However, little is known about the molecular mechanisms underlying osteoclast differentiation in GCTB. Denosumab, a human monoclonal antibody against RANKL, is used for GCTB treatment. Here, we performed morphological and immunohistochemical examinations of pre- and post-denosumab treatment changes by analyzing each stage of osteoclast differentiation.

METHODS

We retrieved 15 archival cases of GCTB with tumor samples from both pre- and post-denosumab treatment. We selected three immunohistochemical markers from the expression data from a previous single-cell RNA study: FOS, a progenitor osteoclast marker, and JDP2 and NFATc1, mature osteoclast markers.

RESULTS

The mean positivity of the markers decreased after denosumab treatment from 11.1% to 8.9% for FOS, from 10.6% to 7.2% for JDP2, and from 10.0% to 0.2% for NFATc1. Only NFATc1 positivity decreased significantly (P < 0.001) after denosumab treatment.

CONCLUSIONS

We identified a new differentiation stage of osteoclast maturation, intermediate cell, by comparing histological findings before and after denosumab treatment. We demonstrated that discrepancies exist between histological and molecular data and highlight the need for establishing an integrated definition of osteoclasts considering morphology and marker expression.

Cytopathology of Chondromyxoid Fibroma: Report of 2 Cases with Immunocytochemical Expression of GRM1

INTRODUCTION

Chondromyxoid fibroma (CMF) is a rare, benign bone tumor that occurs predominantly in the second and third decades of life, more frequently in males. Overexpression of GRM1 as a consequence of tumor-specific gene rearrangement of GRM1 has recently been reported as a useful immunohistochemical marker for histopathological diagnosis of CMF. However, the usefulness of GRM1 staining of cytology specimens has not yet been evaluated. In this report, the cytological findings and GRM1 immunocytochemistry of two cases of CMF are described.

CASE PRESENTATIONS

Case 1 was a 15-year-old girl with a rib tumor. Imaging findings suggested a benign neurogenic tumor such as schwannoma. The tumor had increased in size over a 2-year period and was resected. Case 2 was a 14-year-old boy with a metatarsal tumor involving his left first toe. Imaging findings were suspicious of a benign neoplastic lesion. Biopsy findings suggested a benign tumor, and the patient underwent tumor resection. Cytologically, in both cases the tumor cells were predominantly spindle-shaped or stellate, with a myxoid to chondromyxoid background matrix and multinucleated giant cells, and these matrices were metachromatic with Giemsa staining. Cellular atypia was more accentuated in case 2 than in case 1. Immunocytochemical staining for GRM1 was positive in both cases.

CONCLUSION

Due to the overlap in cytological findings, it is often difficult to differentiate CMF from chondroblastoma and chondrosarcoma grade 2. Immunocytochemical staining for GRM1 may support the diagnosis of CMF, and the reuse of Papanicolaou-stained specimens is applicable. The present cases further demonstrated the difficulty of differentiating CMF from other mimicking tumors such as chondroblastoma and chondrosarcoma grade 2. In such instances, immunocytochemistry for GRM1 is applicable to the diagnostic process, the value of which is strengthened by reusing Papanicolaou-stained specimens.

Multicentric Giant Cell Tumor of Bone

The typical presentation of giant cell tumor of bone is a solitary lesion involving the meta-epiphyseal region of the long bones. The presence of more than one distinct giant cell tumor in the same patient is rare. This study reports on 7 patients with multicentric giant cell tumor of bone. Clinical and radiologic features were reviewed to evaluate the behavior of multicentric giant cell tumor of bone. Immunohistochemistry and genetic analysis for the H3F3A gene were performed to confirm the diagnosis. The knee was most frequently involved, and most of the lesions were in an ipsilateral extremity. All of the patients received surgical management with curettage or resection. The overall median follow-up was 194 months (interquartile range, 41-336 months). Five of 7 patients had local recurrence (71%), but considering the number of surgically treated lesions, the risk of local recurrence was 33% (5 local recurrences among 15 treated lesions). No lung metastases occurred. Multicentric giant cell tumor of bone tends to exhibit the same aggressive clinical behavior as solitary giant cell tumor of bone. Patients should be monitored for the occurrence of other lesions, especially in the ipsilateral extremity. [Orthopedics. 2023;46(6):e376-e380.].

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.

H3G34-mutant diffuse hemispheric glioma with osseous metastases: a case report and literature review

Aim: H3G34 diffuse hemispheric glioma is a CNS tumor that is difficult to diagnose and treat and accompanied with poor prognosis. It is becoming clear that extra CNS metastasis may present in a subset of patients with H3G34 gliomas, further complicating diagnosis and treatment. Materials & methods: We present a case of a 19-year-old female with a H3G34 mutant diffuse hemispheric glioma with osseous metastases. We then provide a literature review of the most recent understanding of H3G34 mutant malignancies. Conclusion: Given the stress that patients with H3G34 can experience and the poor prognosis, it is imperative to expand our knowledge and ascertain accurate diagnostic methodologies and targeted therapeutic approaches.

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.

Expression of SATB2, RUNX2, and SOX9 and possible osteoblastic and chondroblastic differentiation in chondroblastoma

Chondroblastoma (CB) is histologically characterized by oval to polygonal-shaped mononuclear neoplastic cells, multinucleated osteoclastic giant cells, and eosinophilic matrix with occasional calcification. Genetically, the majority of CBs harbor H3F3B p.K36M mutation. Despite the historical nomenclature, it has been reported that the matrix of CB is similar to osteoid rather than true cartilage; however, it remains unclear whether neoplastic cells in CB have the potential for osteoblastic differentiation. To clarify this issue, we immunohistochemically examined the expression of osteogenic and chondrogenic markers (SATB2, RUNX2, p63, and SOX9) as well as H3K36M mutant protein in 33 cases of CB. All 33 cases of CB were positive for H3K36M, while SATB2, RUNX2, p63, and SOX9 were expressed in 30/33 (91%), 33/33 (100%), 29/33 (88%), and 31/32 (97%) CB cases, respectively. Our immunohistochemical results suggest that neoplastic cells in CB frequently express both osteogenic and chondrogenic markers and may have an intermediate feature of osteoblastic and chondroblastic nature.

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.

Progress on Denosumab Use in Giant Cell Tumor of Bone: Dose and Duration of Therapy

Giant cell tumor of bone (GCTB) is an aggressive non-cancerous bone tumor associated with risks of sarcoma and metastasis. Once malignancy occurs, the prognosis is generally poor. Surgery remains the main treatment for GCTB. Multidisciplinary management is a feasible option for patients wherein surgical resection is not an option or for those with serious surgery-related complications. Denosumab is an anti-nuclear factor kappa B ligand approved for the treatment of postmenopausal women with osteoporosis, bone metastases, and advanced or inoperable GCTB. However, the guidelines for treating GCTB are unclear; its short-term efficacy and safety in inoperable patients have been demonstrated. Lengthier therapies (high cumulative doses) or pre-operative adjuvant therapy may be associated with severe complications and high local recurrence rates. Short-term administration helps attain satisfactory local control and functionality. As a result, lately, the impact of different doses and lengths of treatment on the efficacy of denosumab in GCTB treatment, the incidence of complications, and recurrence rates have gained attention. The efficacy and safety of denosumab against GCTB, its impact on imaging assessment, related complications, and recurrence of GCTB were previously reviewed. For further research direction, this paper reviews the progress of studies evaluating the impact of the dose and duration of denosumab therapy for GCTB.

Malignant Transformation of Giant Cell Tumour of Bone: A Review of Literature and the Experience of a Referral Centre

Giant cell tumour of bone (GCTB) is a benign, locally aggressive primary bone neoplasm that represents 5% of all bone tumours. The principal treatment approach is surgery. Although generally GCTB is considered only a locally aggressive disease, it can metastasise, and lung metastases occur in 1–9% of patients. To date, only the use of denosumab has been approved as medical treatment for GCTB. Even more rarely, GCTB undergoes sarcomatous transformation into a malignant tumour (4% of all GCTB), but history of this malignant transformation is unclear and unpredictable. Considering the rarity of the event, the data in the literature are few. In this review, we summarise published data of GCTB malignant transformation and we analyse three cases of malignant transformation of GCTB, evaluating histopathology, genetics, and radiological aspects. Despite the rarity of this event, we conclude that a strict follow up is recommended to detect early malignant transformation.

Nuclear β-catenin translocation plays a key role in osteoblast differentiation of giant cell tumor of bone

Denosumab is a game-changing drug for giant cell tumor of bone (GCTB); however, its clinical biomarker regarding tumor ossification of GCTB has not been elucidated. In this study, we investigated the relationship between Wnt/β-catenin signaling and the ossification of GCTB and evaluated whether endogenous nuclear β-catenin expression predicted denosumab-induced bone formation in GCTB. Genuine patient-derived primary GCTB tumor stromal cells exhibited osteoblastic characteristics. Identified osteoblastic markers and nuclear β-catenin translocation were significantly upregulated via differentiation induction and were inhibited by treating with Wnt signaling inhibitor, GGTI-286, or selective Rac1-LEF inhibitor, NSC23766. Furthermore, we reviewed the endogenous ossification and nuclear β-catenin translocation of 86 GCTB clinical samples and elucidated that intra-tumoral ossification was significantly associated with the nuclear translocation. Three-dimensional quantitative analyses (n = 13) of tumoral CT images have revealed that the nuclear β-catenin translocation of naïve GCTB samples was significantly involved with the denosumab-induced tumor ossification. Our findings suggest a close relationship between the nuclear β-catenin translocation and the osteoblastic differentiation of GCTB. Investigations of the nuclear β-catenin in naïve GCTB samples may provide a promising biomarker for predicting the ossification of GCTB following denosumab treatment.

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.

[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.

Droplet digital PCR-based analyses for robust, rapid, and sensitive molecular diagnostics of gliomas

Classification of gliomas involves the combination of histological features with molecular biomarkers to establish an integrated histomolecular diagnosis. Here, we report on the application and validation of a set of molecular assays for glioma diagnostics based on digital PCR technology using the QX200™ Droplet Digital™ PCR (ddPCR) system. The investigated ddPCR-based assays enable the detection of diagnostically relevant glioma-associated mutations in the IDH1, IDH2, H3-3A, BRAF, and PRKCA genes, as well as in the TERT promoter. In addition, ddPCR-based assays assessing diagnostically relevant copy number alterations were studied, including 1p/19q codeletion, gain of chromosome 7 and loss of chromosome 10 (+ 7/-10), EGFR amplification, duplication of the BRAF locus, and CDKN2A homozygous deletion. Results obtained by ddPCR were validated by other methods, including immunohistochemistry, Sanger sequencing, pyrosequencing, microsatellite analyses for loss of heterozygosity, as well as real-time PCR- or microarray-based copy number assays. Particular strengths of the ddPCR approach are (1) its high analytical sensitivity allowing for reliable detection of mutations even with low mutant allele frequencies, (2) its quantitative determination of mutant allele frequencies and copy number changes, and (3) its rapid generation of results within a single day. Thus, in line with other recent studies our findings support ddPCR analysis as a valuable approach for molecular glioma diagnostics in a fast, quantitative and highly sensitive manner.

Clinicopathological and Molecular Features of Secondary Cancer (Metastasis) to the Thyroid and Advances in Management

Secondary tumours to the thyroid gland are uncommon and often incidentally discovered on imaging. Symptomatic patients often present with a neck mass. Collision tumours of secondary tumours and primary thyroid neoplasms do occur. Ultrasound-guided fine-needle aspiration, core-needle biopsy, and surgical resection with histological and immunohistochemical analysis are employed to confirm diagnosis as well as for applying molecular studies to identify candidates for targeted therapy. Biopsy at the metastatic site can identify mutations (such as EGFR, K-Ras, VHL) and translocations (such as EML4-ALK fusion) important in planning target therapies. Patients with advanced-stage primary cancers, widespread dissemination, or unknown primary origin often have a poor prognosis. Those with isolated metastasis to the thyroid have better survival outcomes and are more likely to undergo thyroid resection. Systemic therapies, such as chemotherapy and hormonal therapy, are often used as adjuvant treatment post-operatively or in patients with disseminated disease. New targeted therapies, such as tyrosine kinase inhibitors and immune checkpoint inhibitors, have shown success in reported cases. A tailored treatment plan based on primary tumour features, overall cancer burden, and co-morbidities is imperative. To conclude, secondary cancer to the thyroid is uncommon, and awareness of the updates on diagnosis and management is needed.

Current management of giant-cell tumor of bone in the denosumab era

Giant-cell tumor of bone is a rare, locally aggressive and rarely metastasizing primary bone tumor. The mainstay of treatment remains controversial and is decided by the balance between adequate surgical margin and sufficient adjacent joint function. Although curettage with a high-speed burr and local adjuvants can maintain normal joint function, many reports have revealed a high local recurrence rate. Conversely, en bloc resection and reconstruction with prostheses for highly aggressive lesions have reportedly lower local recurrence rates and poorer functional outcomes. Denosumab-a full human monoclonal antibody that inhibits receptor activator of nuclear factor-kappa β ligand-was approved by the Food and Drug Authority in 2013 for use in surgically unresectable or when resection is likely to result in severe morbidity for skeletally mature adolescents and adults with giant-cell tumor of bone. However, subsequent studies have suggested that the local recurrence rate would be increased by preoperative use of denosumab. In systematic reviews of the local recurrence rate after preoperative use of denosumab, conclusions vary due to the small sample sizes of the studies reviewed. Therefore, controversy regarding the treatment of giant-cell tumor of bone is ongoing. Here, this review elucidates the management of giant-cell tumor of bone, especially with the local adjuvant and neoadjuvant use of denosumab, and presents the current, evidence-based treatment for giant-cell tumor of bone.

Preoperative Denosumab Therapy Against Giant Cell Tumor of Bone is Associated with an Increased Risk of Local Recurrence After Curettage Surgery

INTRODUCTION

Denosumab has been shown to be highly effective at suppressing the progression of giant cell tumor of bone (GCTB). However, recent studies have observed a potential increased risk of local recurrence after surgery following the use of denosumab, raising concerns on the use of this agent against GCTB in combination with surgery.

METHODS

We retrospectively reviewed the medical records of 234 patients with GCTB who were surgically treated at multiple institutions from 1990 to 2017. Patient background, tumor characteristics, treatment methods, local recurrence-free survival rate, distant metastasis rate, oncologic outcome, and limb function at final follow-up were analyzed and compared between cases treated with and without denosumab.

RESULTS

The 3-year local recurrence-free survival rate was significantly lower in patients who underwent preoperative denosumab therapy (35.3%) compared with those treated without denosumab (79.9%) (P < 0.001). Among patients who were preoperatively treated with denosumab, those who had a local recurrence all underwent curettage surgery.

CONCLUSIONS

Preoperative denosumab therapy in combination with curettage surgery was significantly associated with an increased risk of local recurrence in Campanacci grade 3 tumors. Our data suggest that clinicians seeing GCTB patients should be aware to this increased risk when planning preoperative denosumab therapy.

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.

Post-Denosumab-Treated Giant Cell Tumor of Bone: A Retrospective Histomorphological and Immunohistochemical Study

Introduction Giant cell tumors of bone (GCTBs) are treated with surgery with or without local adjuvants. Denosumab is a human monoclonal antibody that has recently emerged to be effective in treating unresectable and recurrent GCTBs.

Objective In this study, we analyzed the histomorphological changes in GCTB following treatment with denosumab. The expression of histone mutation H3.3G34W by immunohistochemistry (IHC) using mutant specific antibody was also determined.

Materials and Methods Of the total 109 GCTBs encountered during the study period, 14 cases with neoadjuvant denosumab therapy were analyzed retrospectively. The post-treatment changes on histopathology were examined on routine hematoxylin and eosin-stained sections. IHC was done using antihistone H3.3G34 antibodies. Statistical analysis was limited to descriptive statistics. No hypothesis testing was performed.

Results All these cases except three showed fibrosis with areas of hyalinization, prominent newly formed woven bone along with spindle cells in short fascicles and storiform pattern. There was complete absence and marked reduction in osteoclast-like giant cells in six and five patients, respectively. Only three patients showed a substantial amount of residual osteoclast-like giant cells. IHC with antihistone H3.3G34W antibody showed unequivocal nuclear positivity in the mononuclear cells in nine cases. The mononuclear cells rimming and entrapped within the woven bone were also positive on IHC. The spindle cells in the benign fibrous histiocytoma-like areas and septa of aneurysmal bone cyst-like areas also retained nuclear staining.

Conclusion Awareness of post-denosumab-related histopathological changes are necessary to avoid misdiagnosis as fibroosseous lesion and low-grade central osteosarcoma. Expression of mutant-specific H3.3 G34W antibody suggests that the neoplastic stromal cells are largely retained after denosumab therapy. The positive staining of cells both within and those rimming the newly formed woven bone point toward osteoblastic phenotype of the neoplastic stromal cells.

Gene of the month: H3F3A and H3F3B

H3F3A and H3F3B genes are located at 1q42.12 and 17q25.1, respectively, and encode identical H3.3 core histone proteins which form part of the histone hetero-octamer complex. Histones function by packaging DNA into small units, the nucleosome, and are highly susceptible to epigenetic post-translational modification. H3 K27 mutations have been shown to inhibit the polycomb repressive complex 2, which is normally involved in epigenetic gene silencing. Mutations in H3F3A and H3F3B are increasingly recognised in a variety of solid tumours. Point mutations in H3F3A have been described in giant cell tumour of bone and paediatric-type diffuse high-grade gliomas. Mutations in H3F3B have been described in chondroblastoma. Loss of trimethylation of H3 K27 is characteristic of most sporadic and radiation-associated malignant peripheral nerve sheath tumours. Immunohistochemistry with a variety of novel antibodies directed against specific mutations, as well as loss of H3K27me3 staining, may be useful in specific settings and in diagnostically challenging cases.

Sclerostin Immunohistochemical Staining in Aggressive Maxillofacial Giant Cell Lesions: Initial Results and Potential Therapeutic Target

INTRODUCTION

Maxillofacial (MF) giant cell lesions (GCLs) are benign, often locally aggressive lesions with potential for recurrence. Systemic treatments have included interferon alpha, calcitonin, bisphosphonates, and denosumab. Sclerostin (SOST) is typically thought to be a negative regulator of bone metabolism and anti-SOST agents have been used to treat osteoporosis; however, its role in central giant cell granuloma is unknown. The purpose of this study was to evaluate the expression of SOST in MF GCLs.

MATERIALS AND METHODS

This was a retrospective study of patients with MF GCLs treated at a single institution between 1993 and 2008 with a minimum follow-up of 6 months. Representative tissue was used to create a tissue microarray and SOST immunohistochemical (IHC) staining and grading was performed. The primary outcomes were IHC staining of the stromal cells and giant cells. The secondary outcomes included correlation of IHC staining and patient predictor variables including clinically benign and aggressive lesions. All analyses were completed using univariate statistical tests.

RESULTS

A total of 37 subjects were included (29 clinically aggressive and 8 clinically benign). Sclerostin staining was present in 30 of 37 subjects (81%). Of these, 22 (60%) had stromal cell staining and 28 (76%) had giant cell staining. The presence or absence of staining, of either cell type, was not associated with aggressiveness, presence of clinical symptoms, tumor size, previous interferon therapy, previous surgery, or the race or age of the patient.

DISCUSSION

Maxillofacial GCLs have an overall high level of SOST staining; however, the role of SOST in treatment and prognosis is unknown and warrants further study.

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.

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.

Current Concepts in the Treatment of Giant Cell Tumors of Bone

Simple Summary

According to the 2020 World Health Organization classification, a giant cell tumor of bone is an intermediate malignant bone tumor. Denosumab treatment before curettage should be avoided due to the increased risk of local recurrence. Administration of denosumab before en bloc resection of the giant cell tumors of the pelvis and spine facilitates en bloc resection. Nerve-sparing surgery after embolization is a possible treatment for giant cell tumors of the sacrum. Denosumab therapy with or without embolization is indicated for inoperable giant cell tumors of the pelvis, spine, and sacrum. A wait-and-see approach is recommended for lung metastases at first, then denosumab should be administered to the growing lesions. Radiotherapy is not recommended owing to the risk of malignant transformation. Local recurrence after 2 years or more should be indicative of malignant transformation. This review summarizes the treatment approaches for non-malignant and malignant giant cell tumors of bone.

Abstract

The 2020 World Health Organization classification defined giant cell tumors of bone (GCTBs) as intermediate malignant tumors. Since the mutated H3F3A was found to be a specific marker for GCTB, it has become very useful in diagnosing GCTB. Curettage is the most common treatment for GCTBs. Preoperative administration of denosumab makes curettage difficult and increases the risk of local recurrence. Curettage is recommended to achieve good functional outcomes, even for local recurrence. For pathological fractures, joints should be preserved as much as possible and curettage should be attempted. Preoperative administration of denosumab for pelvic and spinal GCTBs reduces extraosseous lesions, hardens the tumor, and facilitates en bloc resection. Nerve-sparing surgery after embolization is a possible treatment for sacral GCTBS. Denosumab therapy with or without embolization is indicated for inoperable pelvic, spinal, and sacral GCTBs. It is recommended to first observe lung metastases, then administer denosumab for growing lesions. Radiotherapy is associated with a risk of malignant transformation and should be limited to cases where surgery is impossible and denosumab, zoledronic acid, or embolization is not available. Local recurrence after 2 years or more should be indicative of malignant transformation. This review summarizes the treatment approaches for non-malignant and malignant GCTBs.

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.

Giant cell tumor of bone - Analysis of 213 cases involving extra-craniofacial bones

We elucidated clinicopathological characteristics of giant cell tumor of bone (GCTB) in Japan, and significant clinicopathological factors for predicting local recurrence. Clinicopathological profiles of 213 patients with GCTB (100 male, 113 female) involving extra‐craniofacial bones were retrieved. Pathological slides obtained at the initial surgery were reviewed. Fourteen pathological and five clinical features were statistically analyzed to disclose prognostic significance. Patient age ranged from 12–80 years (Average 38.7). Long bones were most frequently affected (86.4%), especially around the knee (62.9%). Histological features are basically similar to those previously reported. Within a follow‐up period (24–316 months, average 106.1 months), the local recurrence rate is 29.1%. Metastasis has occurred in 9 patients. Cox regression analysis of representative clinicopathological features shows that younger age, higher mitotic count, smaller zones of stromal hemorrhage, considerable vascular invasion and absence of ischemic necrosis are significant predictors for local recurrence. Initial operative method (curettage) is a significant risk factor in univariate analysis but not by multivariate analysis (P = 0.053). Denosumab administration increases risk but not significantly (P = 0.053). Histone 3.3 G34W immunopositivity is not significant for predicting local recurrence.