Malignant Tenosynovial Giant Cell Tumor: The True "Synovial Sarcoma?" A Clinicopathologic, Immunohistochemical, and Molecular Cytogenetic Study of 10 Cases, Supporting Origin from Synoviocytes

MR Imaging of the Hip: Infectious and Inflammatory Conditions

MR imaging is a useful tool in establishing the diagnosis of inflammation and/or infection in the hip joint and adjacent tissues, and in determining the extent of disease. In conjunction with clinical factors, MR imaging findings can help to narrow the differential diagnosis in individual cases and can guide decisions regarding biopsies, aspirations, or additional imaging.

Localized type tenosynovial giant cell tumor with metastases to lungs and pleura: a case report and literature review

BACKGROUND

Tenosynovial giant cell tumor is a rare soft tissue tumor of the synovium of joint, bursae, or tendon sheath. It is divided into localized or diffuse types on the basis of the growth pattern. Localized tenosynovial giant cell tumors are usually benign and treated successfully by excision. Diffuse tenosynovial giant cell tumors, in contrast to localized type, can destroy bone and cartilage and are associated with frequent local recurrences and distant metastasis. Localized type tenosynovial giant cell tumors rarely metastasize to distant organs. Here, we report a case of localized tenosynovial giant cell tumor presenting with lung metastases and systematically review literature.

CASE PRESENTATION

A 55-year-old Asian male presented with a dry cough, right-sided chest pain and progressive dyspnea for 1 month. At 18 months before this presentation, he had undergone excision of a painless swelling on his right index finger. The swelling recurred within 3 months of excision, and a biopsy was then suggestive of a giant cell tumor. Given the suspicion of a giant cell tumor, a wide excision of the lesion was performed and the excisional biopsy was consistent with a diagnosis of tenosynovial giant cell tumor, localized type. At admission to our hospital, the patient had tachypnoea and absent breath sounds on the right side. A chest radiograph showed a right-sided pleural effusion with a homogenous opacity in the left mid-zone. A contrast-enhanced computed tomography of the chest and abdomen showed right massive pleural effusion and bilateral multiple lobulated heterogeneously enhancing pleural-based masses with areas of internal calcification. Pleural fluid analysis revealed an exudate with no malignant cells on cytology. A lung biopsy showed osteoclast-like giant cells and mononuclear spindle cells with areas of hemorrhage and necrosis, suggesting tenosynovial giant cell tumor metastasis. A final diagnosis of localized type tenosynovial giant cell tumor of the right index finger with metastases to the lungs and pleura was made. The patient passed away after receiving three cycles of denosumab injection owing to progressive disease.

CONCLUSION

Lung metastasis is extremely rare in patients with localized tenosynovial giant cell tumor. The survival is usually poor in patients with lung metastasis. A close follow-up of patients with localized type tenosynovial giant cell tumor is necessary for early detection of pleuropulmonary complications.

Pathology of intra-articular tumours and tumour-like lesions: pearls, pitfalls and rarities from a general surgical pathology practice

Intra-articular tumours are uncommonly encountered in routine practice and may present diagnostic challenges to pathologists. Challenges unique to this site include distinction from more common reactive synovial conditions, which are far more common; histologic variability; superimposed reactive changes; and often, lack of provided clinicoradiological context. This article reviews the pathology of the synovial tumours and tumour-like lesions, including diagnostic pearls, pitfalls and rare entities.

Chondroid Synoviocytic Neoplasm: A Clinicopathologic, Immunohistochemical, and Molecular Genetic Study of a Distinctive Tumor of Synoviocytes

Tumors resembling tenosynovial giant cell tumor (TGCT) but additionally forming chondroid matrix are rare and most often involve the temporomandibular joint (TMJ). We studied 21 tumors consisting of synoviocytes (large, eosinophilic mononuclear cells containing hemosiderin) and chondroid matrix to better understand these unusual neoplasms. The tumors occurred in 10 males and 11 females, in the age group of 31 to 80 years (median, 50 years) and involved the TMJ region (16), extremities (4), and spine (1). As in conventional TGCT, all were composed of synoviocytes, small histiocytes, foamy macrophages, siderophages, and osteoclast-like giant cells in variably hyalinized background. Expansile nodules of large, moderately atypical synoviocytes were present, in addition to "chondroblastoma-like," "chondroma-like," or "phosphaturic mesenchymal tumor-like" calcified matrix. The synoviocytes expressed clusterin (17/19) and less often desmin (3/15). The tumors were frequently CSF1 positive by chromogenic in situ hybridization (8/13) but at best weakly positive for CSF1 by immunohistochemistry (0/3). Background small histiocytes were CD163 positive (12/12). All were FGF23 negative (0/10). Cells within lacunae showed a synoviocytic phenotype (clusterin positive; S100 protein and ERG negative). RNA-Seq was successful in 13 cases; fusions were present in 7 tumors, including FN1::TEK (5 cases); FN1::PRG4 (2 cases); and MALAT1::FN1, PDGFRA::USP35, and TIMP3::ZCCHC7 (1 case each). Three tumors contained more than 1 fusion (FN1::PRG4 with TIMP3::ZCCHC7, FN1::TEK with FN1::PRG4, and FN1::TEK with MALAT1::FN1). Clinical follow-up (17 patients; median follow-up duration 38 months; range 4-173 months) showed 13 (76%) to be alive without evidence of disease and 4 (24%) to be alive with persistent/recurrent local disease. No metastases or deaths from disease were observed. We conclude that these unusual tumors represent a distinct category of synoviocytic neoplasia, which we term "chondroid synoviocytic neoplasm," rather than simply ordinary TGCT with cartilage. Despite potentially worrisome morphologic features, they appear to behave in at most a locally aggressive fashion.

Keratin-Positive Giant Cell Tumor of Bone and Soft Tissue With HMGA2::NCOR2 Fusion in Children Under 10 With Response to Imatinib Therapy: A Case Series

HMGA2::NCOR2 keratin-positive giant cell tumors in children with response to imatinib in an infant.

Current therapies and future prospective for locally aggressive mesenchymal tumors

Locally aggressive mesenchymal tumors comprise a heterogeneous group of soft tissue and bone tumors with intermediate histology, incompletely understood biology, and highly variable natural history. Despite having a limited to absent ability to metastasize and excellent survival prognosis, locally aggressive mesenchymal tumors can be symptomatic, require prolonged and repeat treatments including surgery and chemotherapy, and can severely impact patients' quality of life. The management of locally aggressive tumors has evolved over the years with a focus on minimizing morbid treatments. Extensive oncologic surgeries and radiation are pillars of care for high grade sarcomas, however, play a more limited role in management of locally aggressive mesenchymal tumors, due to propensity for local recurrence despite resection, and the risk of transformation to a higher-grade entity following radiation. Patients should ideally be evaluated in specialized sarcoma centers that can coordinate complex multimodal decision-making, taking into consideration the individual patient's clinical presentation and history, as well as any available prognostic factors into customizing therapy. In this review, we aim to discuss the biology, clinical management, and future treatment frontiers for three representative locally aggressive mesenchymal tumors: desmoid-type fibromatosis (DF), tenosynovial giant cell tumor (TSGCT) and giant cell tumor of bone (GCTB). These entities challenge clinicians with their unpredictable behavior and responses to treatment, and still lack a well-defined standard of care despite recent progress with newly approved or promising experimental drugs.

One-Stage Synovectomies Result in Improved Short-Term Outcomes Compared to Two-Stage Synovectomies of Diffuse-Type Tenosynovial Giant Cell Tumor (D-TGCT) of the Knee: A Multicenter, Retrospective, Cohort Study

Diffuse-type tenosynovial giant cell tumors' (D-TGCTs) intra- and extra-articular expansion about the knee often necessitates an anterior and posterior surgical approach to facilitate an extensive synovectomy. There is no consensus on whether two-sided synovectomies should be performed in one or two stages. This retrospective study included 191 D-TGCT patients from nine sarcoma centers worldwide to compare the postoperative short-term outcomes between both treatments. Secondary outcomes were rates of radiological progression and subsequent treatments. Between 2000 and 2020, 117 patients underwent one-stage and 74 patients underwent two-stage synovectomies. The maximum range of motion achieved within one year postoperatively was similar (flexion 123-120°, p = 0.109; extension 0°, p = 0.093). Patients undergoing two-stage synovectomies stayed longer in the hospital (6 vs. 4 days, p < 0.0001). Complications occurred more often after two-stage synovectomies, although this was not statistically different (36% vs. 24%, p = 0.095). Patients treated with two-stage synovectomies exhibited more radiological progression and required subsequent treatments more often than patients treated with one-stage synovectomies (52% vs. 37%, p = 0.036) (54% vs. 34%, p = 0.007). In conclusion, D-TGCT of the knee requiring two-side synovectomies should be treated by one-stage synovectomies if feasible, since patients achieve a similar range of motion, do not have more complications, but stay for a shorter time in the hospital.

Best clinical management of tenosynovial giant cell tumour (TGCT): A consensus paper from the community of experts

Tenosynovial giant cell tumour (TGCT) is a rare, locally aggressive, mesenchymal tumor arising from the joints, bursa and tendon sheaths. TGCT comprises a nodular- and a diffuse-type, with the former exhibiting mostly indolent course and the latter a locally aggressive behavior. Although usually not life-threatening, TGCT may cause chronic pain and adversely impact function and quality of life (QoL). CSFR1 inhibitors are effective with benefit on symptoms and QoL but are not available in most countries. The degree of uncertainty in selecting the most appropriate therapy and the lack of guidelines on the clinical management of TGCT make the adoption of new treatments inconsistent across the world, with suboptimal outcomes for patients. A global consensus meeting was organized in June 2022, involving experts from several disciplines and patient representatives from SPAGN to define the best evidence-based practice for the optimal approach to TGCT and generate the recommendations presented herein.

Diagnostic utility of CSF1 immunohistochemistry in tenosynovial giant cell tumor for differentiating from giant cell-rich tumors and tumor-like lesions of bone and soft tissue

BACKGROUND

Tenosynovial giant cell tumor (TSGCT) is a benign fibrohistiocytic tumor that affects the synovium of joints, bursa, and tendon sheaths and is categorized into localized TSGCT (LTSGCT) and diffuse TSGCT (DTSGCT). LTSGCT and DTSGCT are characterized by recurrent fusions involving the colony-stimulating factor 1 (CSF1) gene and its translocation partner collagen type VI alpha 3 chain. The fusion gene induces intratumoral overexpression of CSF1 mRNA and CSF1 protein. CSF1 expression is a characteristic finding of TSGCT and detection of CSF1 mRNA and CSF1 protein may be useful for the pathological diagnosis. Although there have been no effective anti-CSF1 antibodies to date, in situ hybridization (ISH) for CSF1 mRNA has been performed to detect CSF1 expression in TSGCT. We performed CSF1 immunohistochemistry (IHC) using anti-CSF1 antibody (clone 2D10) in cases of TSGCT, giant cell-rich tumor (GCRT), and GCRT-like lesion and verified its utility for the pathological diagnosis of TSGCT.

METHODS

We performed CSF1 IHC in 110 cases including 44 LTSGCTs, 20 DTSGCTs, 1 malignant TSGCT (MTSGCT), 10 giant cell tumors of bone, 2 giant cell reparative granulomas, 3 aneurysmal bone cysts, 10 undifferentiated pleomorphic sarcomas, 10 leiomyosarcomas, and 10 myxofibrosarcomas. We performed fluorescence ISH (FISH) for CSF1 rearrangement to confirm CSF1 expression on IHC in TSGCTs. We considered the specimens to have CSF1 rearrangement if a split signal was observed in greater than 2% of the tumor cells.

RESULTS

Overall, 50 of 65 TSGCT cases, including 35 of the 44 LTSGCTs and 15 of the 20 DTSGCTs, showed distinct scattered expression of CSF1 in the majority of mononuclear tumor cells. MTSGCT showed no CSF1 expression. Non-TSGCT cases were negative for CSF1. FISH revealed CSF1 rearrangement in 6 of 7 CSF1-positive cases on IHC. On the other hand, FISH detected no CSF1 rearrangement in all CSF1-negative cases on IHC. Thus, the results of IHC corresponded to those of FISH.

CONCLUSION

We revealed characteristic CSF1 expression on IHC in cases of TSGCT, whereas the cases of non-TSGCT exhibited no CSF1 expression. CSF1 IHC may be useful for differentiating TSGCTs from histologically mimicking GCRTs and GCRT-like lesions.

Surgical management of 144 diffuse-type TGCT patients in a single institution: A 20-year cohort study

BACKGROUND AND OBJECTIVES

Surgery is the mainstay of treatment for tenosynovial giant cell tumors (TGCTs). However, achieving a cure through surgery alone remains challenging, especially for the diffuse-type (D-TGCT).

METHODS

Our goal was to describe the surgical management of patients with D-TGCT related to large joints, treated between 2000 and 2020. We analyzed the effect of (in)complete resections and the presence of postoperative tumor (POT) on magnetic resonance imaging (MRI) on radiological and clinical outcomes.

RESULTS

A total of 144 patients underwent open surgery for D-TGCT, of which 58 (40%) had treatment before. The median follow-up was 65 months. One hundred twenty-five patients underwent isolated open surgeries, in which 25 (20%) patients' D-TGCT was intentionally removed incompletely. POT presence on the first postoperative MRI was observed in 64%. Both incomplete resections and POT presence were associated with higher rates of radiological progression (73% vs. 44%; Kaplan-Meier [KM] analysis p = 0.021) and 59% versus 7%; KM analysis p < 0.001), respectively. Furthermore, patients with POT presence clinically worsened more often than patients without having POT (49% vs. 24%; KM analysis p = 0.003).

CONCLUSIONS

D-TGCT is often resected incompletely and tumor presence is commonly observed on the first postoperative MRI, resulting in worse radiological and clinical outcomes. Therefore, surgeons should try to remove D-TGCT in toto and consider other multimodal therapeutic strategies.

Malignant Diffuse-Type Tenosynovial Giant Cell Tumor in the Subcutaneous Tissue of the Midthigh: A Report of a Rare Tumor in an Unusual Location

Malignant TS-GCT is an extremely rare and aggressive tumor with only few cases published in the literature, due to the small number of cases is not completely understood and is diagnostically challenging. Although surgical treatment is the primary treatment modality, there is no consensus regarding adjuvant treatment. Regardless of mode of treatment, the tumor still caries unfavorable prognosis. In this paper, we reviewed the literature for cases of malignant TS-GCT. We also would like to present an additional case of malignant TS-GCT that was found in an unusual location in subcutaneous tissue of the midthigh.

PD-L1 Status in Tenosynovial Giant Cell Tumors

Background and Objectives: Tenosynovial giant cell tumors (TSGCTs) are benign soft tissue tumors that are divided into localized- and diffuse-type tumors, according to the World Health Organization classification of soft tissue tumours. The diffuse-type TSGCT sometimes behave aggressively and poses treatment challenges especially in patients with neurovascular involvement. Symptomatic patients who are not good candidates for surgery due to high morbidity risk may benefit from medical therapy. Objectives: Drugs that target programmed death ligand 1 (PD-L1) are among a new generation of medical therapy options, which, recently, have been explored and have displayed promising results in various cancer types; therefore, we aimed to investigate the PD-L1 status of TSGCTs as a possible therapeutic target. Materials and Methods: We assessed the PD-L1 status of 20 patients (15 men and 5 women, median age = 39 years) that had been diagnosed with TSGCTs in a single institution, between 2018 and 2020. The patients had localized- (n = 7) and diffuse-type (n = 13) TSGCTs. Formalin-fixed paraffin-embedded (FFPE) blocks were retrospectively retrieved from the pathology department. An immunohistochemical analysis was performed in sections of 3 micron thickness from these blocks. Results: Seventy-five percent of our patients with TSGCTs were immunopositive to PD-L1 staining. Conclusions: Taking into consideration the high positivity rate of PD-L1 staining in TSGCTs, PD-L1 blockage may be used as a valuable medical treatment for TSGCTs; however, further studies are needed.

Long-term follow-up of nilotinib in patients with advanced tenosynovial giant cell tumours: Long-term follow-up of nilotinib in TGCT

BACKGROUND

Diffuse-type tenosynovial giant cell tumour (D-TGCT) is a non-malignant but locally aggressive tumour driven by overexpression of colony-stimulating factor-1 (CSF1). CSF1R inhibitors are potential therapeutic strategies for patients not amenable to surgery. We report here the long-term outcome of nilotinib in patients with advanced D-TGCT treated within a phase II prospective international study (ClinicalTrials.gov: NCT01261429).

METHODS

Patients were enrolled between December 2010-September 2012 at 11 cancer centres. Eligible patients had histologically confirmed D-TGCT, not amenable to surgery. Patients received nilotinib until evidence of progression, toxicity or a maximum of one year. Long-term data were retrospectively collected after the completion of the phase II trial. Patients with nilotinib treatment ≥12 weeks and follow-up ≥12 months were included for long-term analysis.

RESULTS

Forty-eight of 56 enrolled patients were included. Median treatment duration was 11 months; 31 (65%) patients completed the treatment protocol. After 102 months of follow-up (median; range 12-129), 25 patients (52%) had progression. The median progression-free survival (PFS) was 77 months. The five-year PFS rate was 53%. Fifteen patients (n = 15/46; 33%) experienced clinical worsening after 11 months (median). Twenty-seven patients (58%) received additional treatment, after which eleven patients (n = 11/27; 41%) had a second relapse. Nine patients required a subsequent treatment, primarily other CSF1R inhibitors (n = 6/9; 67%). No unfavourable long-term effects were observed.

CONCLUSION

This long-term analysis of nilotinib for advanced D-TGCT showed that about half of the patients had progression and underwent additional treatment after 8.5 years follow-up. Contrarily, several patients had ongoing disease control after limited treatment duration, demonstrating the mixed effect of nilotinib.

Neoplastic synovial lining cells that coexpress podoplanin and CD90 overproduce CSF-1, driving tenosynovial giant cell tumor

Tenosynovial giant cell tumor (TCGT) is a rare neoplasm affecting the synovium of joints, bursae, and tendon sheaths. The overproduction of colony-stimulating factor-1 (CSF-1) by a minority of the tumor population works in a paracrine fashion to drive tumor growth. Pathology of the reactive, monocytic component has been well elucidated, whereas the populations of neoplastic cells and all the sources of CSF-1 overproduction are incompletely characterized. Podoplanin (PDPN), or gp38, is a cell surface glycoprotein that is expressed on fibroblast-like synovial cells and upregulated in rheumatoid arthritis and many cancers; it governs cell mobility, epithelial-mesenchymal transition, and other functions and is associated with lymphangiogenesis and poor prognosis in many solid tumors, which underscores its local and possible systemic effects. We found higher PDPN expression in TGCT than in internal controls of patients' healthy synovium. Flow cytometry partitioned PDPN^high cells into PDPN^high CD90⁺ and PDPN^high CD14⁺ populations. Quantitative real-time polymerase chain reaction analysis of the PDPN^high CD90⁺ cells revealed that CSF-1 expression was 10-fold higher than in PDPN^high CD14⁺ cells. Therefore, we conclude that the lining fibroblast-like synovial cells, which express PDPN^high CD90⁺ , are responsible for the overproduction of CSF-1 and for driving tumor growth.

Tenosynovial giant cell tumors (TGCT): molecular biology, drug targets and non-surgical pharmacological approaches

INTRODUCTION

Tenosynovial giant cell tumor (TGCT) is a mono-articular, benign or locally aggressive and often debilitating neoplasm. Systemic therapies are becoming part of the multimodal armamentarium when surgery alone will not confer improvements. Since TGCT is characterized by colony-stimulating factor-1 (CSF1) rearrangements, the most studied molecular pathway is the CSF1 and CSF1 receptor (CSF1R) axis. Inhibiting CSF1-CSF1R interaction often yields considerable radiological and clinical responses; however, adverse events may cause treatment discontinuation because of an unfavorable risk-benefit ratio in benign disease. Only Pexidartinib is approved by the US FDA; however, the European Medicines Agency has not approved it due to uncertainties on the risk-benefit ratio. Thus, there is a need for safer and effective therapies.

AREAS COVERED

Light is shed on disease mechanisms and potential drug targets. The safety and efficacy of different systemic therapies are evaluated.

EXPERT OPINION

The CSF1-CSF1R axis is the principal drug target; however, the effect of CSF1R inhibition on angiogenesis and the role of macrophages, which are essential in the postoperative course, needs further elucidation. Systemic therapies have a promising role in treating mainly diffuse-type, TGCT patients who are not expected to clinically improve from surgery. Future drug development should focus on targeting neoplastic TGCT cells.

Update on Tenosynovial Giant Cell Tumor, an Inflammatory Arthritis With Neoplastic Features

Rheumatoid arthritis (RA) is a chronic inflammatory disease that leads to joint destruction and bone erosion. Even if many treatments were developed with success in the last decades, some patients fail to respond, and disease chronicity is still a burden. Mechanisms involved in such resistance may include molecular changes in stromal cells. Other explanations can come from observations of tenosynovial giant cell tumor (TGCT), first considered as an inflammatory arthritis, but with unusual neoplastic features. TGCT leads to synovium hypertrophy and hyperplasia with hemosiderin deposition. It affects young adults, resulting in secondary osteoarthritis and increased morbidity. TGCT shows clinical, histological and genetic similarities with RA but affecting a single joint. However, the monoclonality of some synoviocytes, the presence of translocations and rare metastases also suggest a neoplastic disease, with some features common with sarcoma. TGCT is more probably in an intermediate situation between an inflammatory and a neoplastic process, with a main involvement of the proinflammatory cytokine CSF-1/CSF1R signaling axis. The key treatment option is surgery. New treatments, derived from the RA and sarcoma fields, are emerging. The tyrosine kinase inhibitor pexidartinib was recently FDA-approved as the first drug for severe TGCT where surgery is not an option. Options directly targeting the excessive proliferation of synoviocytes are at a preclinical stage.

Role of colony-stimulating factor 1 in the neoplastic process of tenosynovial giant cell tumor

Tenosynovial giant cell tumors (TGCTs) are rare, locally aggressive, mesenchymal neoplasms, most often arising from the synovium of joints, bursae, or tendon sheaths. Surgical resection is the first-line treatment, but recurrence is common, with resulting impairments in patients' mobility and quality of life. Developing and optimizing the role of systemic pharmacologic therapies in TGCT management requires an understanding of the underlying disease mechanisms. The colony-stimulating factor 1 receptor (CSF1R) has emerged as having an important role in the neoplastic processes underlying TGCT. Lesions appear to contain CSF1-expressing neoplastic cells derived from the synovial lining surrounded by non-neoplastic macrophages that express the CSF1R, with lesion growth stimulated by both autocrine effects causing proliferation of the neoplastic cells themselves and by paracrine effects resulting in recruitment of CSF1 R-bearing macrophages. Other signaling pathways with evidence for involvement in TGCT pathogenesis include programmed death ligand-1, matrix metalloproteinases, and the Casitas B-cell lymphoma family of ubiquitin ligases. While growing understanding of the pathways leading to TGCT has resulted in the development of both regulatory approved and investigational therapies, more detail on underlying disease mechanisms still needs to be elucidated in order to improve the choice of individualized therapies and to enhance treatment outcomes.

Malignant Tenosynovial Giant Cell Tumor Presenting as an Extra-Articular Superficial Soft-Tissue Mass in a Knee

Malignant tenosynovial giant cell tumor (TsGCT) is a rare disease that can arise as a recurrent lesion or co-exist with a benign TsGCT lesion. Here we report a rare case of malignant TsGCT in a 73-year-old male with a history of lymphoma. The tumor appeared as a superficial soft-tissue mass in the subcutaneous fat tissue of the left knee.

Molecular targeted therapy for advanced or metastatic soft tissue sarcoma

Soft tissue sarcomas are a form of rare and heterogeneous neoplasms with high recurrence rate and mortality. Over the past decades, less progress has been achieved. Surgical management with or without adjuvant/neoadjuvant radiotherapy is still the first-line treatment for localized soft tissue sarcomas, and chemotherapy is the additional option for those with high-risk. However, not all patients with advanced or metastatic soft tissue sarcomas benefit from conventional chemotherapy, targeted therapy takes the most relevant role in the management of those resistant to or failed to conventional chemotherapy. Heterogeneous soft tissue sarcomas vary from biological behavior, genetic mutations, and clinical presentation with a low incidence, indicating the future direction of histotype-based even molecule-based personalized therapy. Furthermore, increasing preclinical studies were carried out to investigate the pathogenesis and potential therapeutic targets of soft tissue sarcomas and increasing new drugs have been developed in recent years, which had started opening new doors for clinical treatment for patients with advanced/metastatic soft tissue sarcomas. Here we sought to summarize the concise characteristics and advance in the targeted therapy for the most common subtypes of soft tissue sarcomas.

Intra-Articular Tumors

The intra-articular space is a relatively rare site of occurrence of neoplastic diseases. The 2 distinct groups of clinicopathologic entities that exhibit an almost exclusive tropism for the joints are represented by synovial chondromatosis and tenosynovial giant cell tumors (TGCT). Synovial chondromatosis is a locally aggressive chondrogenic neoplasm that very rarely can show malignant behavior. TGCT occur in 2 main variants, the localized variant and the more locally aggressive diffuse type. Malignant TCGT is exceedingly rare and is characterized by significant rates of both local recurrence and metastatic spread.

Intramuscular Tenosynovial Giant Cell Tumor Harboring a Novel CSF1-CD96 Fusion Transcript

Tenosynovial giant cell tumors typically arise in the synovium of joints, bursae, or tendon sheaths. They may occur in an intra- or extra-articular location and can be divided into localized and diffuse types. The neoplastic nature of the lesion has been supported by a recurrent CSF1 gene rearrangement in a small subset of lesional cells, of which the most common fusion partner is COL6A3. Herein, we report a case of intramuscular localized tenosynovial giant cell tumor harboring a novel CSF1-CD96 fusion transcript, thus expanding the molecular profile of this tumor.

Clinical comparison of tenosynovial giant cell tumors, synovial chondromatosis, and synovial sarcoma: analysis and report of 53 cases

Background

Tenosynovial giant cell tumors (TGCTs), synovial chondromatosis (SC), and synovial sarcoma (SS) exhibit similarities in clinical features and histochemical characteristics, and differential diagnosis remains challenging in clinical practice.

Methods

Data were collected from the pathology database of Shanghai Ninth People's Hospital regarding patients who underwent surgery from 2010 to 2019 with histologically confirmed TGCTs, SC, and SS. Demographic and clinicopathological data of these patients were reviewed. Immunohistochemistry staining of 14 different markers was performed. Correlation analyses of the prognoses were evaluated.

Results

A total of 26 patients with TGCTs (8 diffuse TGCTs and 18 localized TGCTs), 16 with SC, and 11 with SS were identified. Pain was the main symptom of patients with both TGCTs and SC, while a palpable mass was the most common symptom for patients with SS. In addition to clinical features, we identified vital risk factors for disease recurrence. The mean follow-up periods were 51, 39, and 14 months for TGCTs, SC, and SS, respectively. Younger patients with diffuse TGCTs or patients with a higher neutrophil/lymphocyte ratio (NLR) displayed a significantly higher frequency of recurrence. We also plotted receiver operating characteristic (ROC) curve analysis for age and NLR. The area under the ROC curve (AUC) was calculated and demonstrated the ability to distinguish recurrent from nonrecurrent cases. In addition, higher CD163 expression was linked to recurrent diffuse TGCT cases.

Conclusions

These data indicated possible characteristics of different aspects of TGCTs, SC, and SS. Further clarification and understanding of these factors will help with differential clinical diagnosis and recurrent risk assessment.

Giant cell tumour of the tendon sheath of the spine: clinical features and imaging findings

Objectives

To review the clinical and imaging data of spinal giant cell tumour of the tendon sheath (GCTTS) to improve our understanding of the disease.

Methods

The imaging findings, clinicopathological features and clinical outcomes of 14 patients with pathologically confirmed spinal GCTTS were analysed retrospectively.

Results

All 14 patients had a single spinal lesion, including ten cervical vertebra lesions and four thoracic vertebra lesions. CT scan findings: The lesions showed osteolytic bone destruction and were centred on the facet joint, eroding the surrounding bone with a paravertebral soft tissue mass. MRI scan findings: all the lesions manifested predominantly as isointense or hypointense on T1-weighted imaging (T1WI). On T2-weighted imaging (T2WI), eight lesions were hypointense, and four were isointense. The remaining two lesions showed slight hyperintensity. The enhanced scans of eight lesions showed moderate to marked homogeneous or heterogeneous enhancement. PET/CT findings: Among the five patients who underwent PET/CT, three presented lesions with well-defined, sclerotic borders, and the uptake of ¹⁸F-FDG was markedly increased. One lesion showed an ill-defined border and an uneven increase in ¹⁸F-FDG uptake with an SUVmax value of 8.9. A recurrent lesion was only found on PET/CT 45 months after surgery and the SUVmax was 5.1.

Conclusions

Spinal GCTTS is extremely rare. Osteolytic bone destruction in the area of the facet joint with a soft tissue mass and hypointensity on T2WI images are indicative of the spinal GCTTS. GCTTS shows high uptake of ¹⁸F-FDG, and PET/CT is helpful in detecting recurrent lesions.

RNAscope CSF1 chromogenic in situ hybridization: a potentially useful tool in the differential diagnosis of tenosynovial giant cell tumors

Colony stimulating factor-1 (CSF1) upregulation and CSF1/colony-stimulating factor 1 receptor (CSF1R) signaling pathway is central to the tumorigenesis of tenosynovial giant cell tumors (TGCT) of both localized (LTGCT) and diffuse (DTGCT) types, and has been demonstrated in a small number of malignant tumors (MTGCT) as well. In situ hybridization for CSF1 mRNA has been shown to be potentially useful in the diagnosis of TGCT, although only a relatively small number of cases have been studied. We studied CSF1 mRNA expression using RNAscope chromogenic in situ hybridization (CISH) in standard tissue sections from 31 TGCT and 26 non-TGCT, and in tumor microarray slides (Pantomics normal MN0341, Pantomics tumor MTU391, Pantomics melanoma MEL961). Among normal tissues, CSF1 mRNA expression was invariably present in synovium (10/10, 100%) and absent in all other normal tissues. All LTGCT and DTGCT were positive (24/24, 100%), exclusively in large, eosinophilic synoviocytes. MTGCT contained large clusters of CSF1-positive malignant synoviocytes (8/8, 100%); malignant spindled cells were also positive. Among non-TGCT, CSF1 CISH was less often positive with high specificity (90%). CSF1-positive cases included leiomyosarcoma, giant cell tumor of bone and of soft parts, pulmonary carcinoma and others. The sensitivity and specificity of RNAscope CSF1 mRNA CISH for the diagnosis of TGCT were 100% and 90%, respectively. We conclude that RNAscope CSF1 CISH may be a valuable adjunct for the diagnosis of TGCT of all types, especially those with atypical or malignant morphologic features. Detection of CSF1 mRNA expression may also have predictive significance in cases where use of the CSF1 inhibitor pexidartinib is considered.

Chronic lymphoplasmacytic villonodular proliferative synovitis in a 10-year-old Jack Russell Terrier dog

We describe a case of chronic lymphoplasmacytic villonodular synovitis (CLPVNS) associated with cranial cruciate ligament (CCL) disease in a 10-year-old spayed Jack Russell Terrier bitch. The bitch was presented to a veterinary clinic with severe, non-weight bearing, acute left hindlimb lameness. The bitch had previously been treated surgically for stifle CCL disease of the same joint, using the lateral fabellar suture (LFS) technique. Since the treatment, the patient had a history of intermittent left hindlimb non-weight bearing lameness that was manageable with nonsteroidal anti-inflammatory drugs (NSAIDs). Palpation and manipulation of the affected stifle elicited severe pain. There were no other clinical or orthopaedic abnormalities. Orthogonal radiographs of the affected stifle revealed moderate degenerative joint disease and osteolytic lesions on the lateral aspect of the lateral femoral condyle and the head of the fibula. A fluid aspirate from this joint was negative for bacterial growth on culture. Cytology results were suspicious for CLPVNS. Exploratory arthrotomy, synovectomy, debridement and lavage of the affected joint were performed. Bone and synovial membrane biopsy samples of the joint were obtained and submitted to a laboratory for a histopathological confirmatory diagnosis. CLPVNS was tentatively diagnosed by cytology, and confirmed by histopathology of biopsy samples. This case report highlights the importance of checking for CLPVNS in dogs with lameness associated with CCL disease, as reports show it to be underreported or misdiagnosed.

Uncommon tumors of temporomandibular joint: An institutional experience and review

BACKGROUND

The temporomandibular joint (TMJ) harbors a myriad of pathologic alterations including arthritides and benign and malignant neoplasms.

METHODS

Herein, we describe our institutional experience of some uncommon and unusual synovial pathologies of the TMJ along with a review of literature. We searched through the archives of department of pathology and institutional electronic medical record for specimens of TMJ between 1999 and 2019. Hematoxylin and eosin slides were reviewed and data (final diagnosis, age, gender, clinical presentation, tumor size, treatment modality, recurrence, and vital status) were collected.

RESULTS

A total of seven cases were identified including four cases of synovial chrondromatosis; and one case each of tenosynovial giant cell tumor, localized type, tenosynovial giant cell tumor, diffuse type, and synovial sarcoma.

CONCLUSIONS

The article emphasizes on the clinical, radiologic, pathologic, and molecular features of these uncommon entities. The differential diagnosis of each entity is also discussed. Current updates in the management are also reviewed.

Soft Tissue Special Issue: Giant Cell-Rich Lesions of the Head and Neck Region

Giant cell-rich lesions represent a heterogeneous group of tumors and non-neoplastic lesions, usually arising in bone, which harbor varying number of reactive osteoclastic-type multinucleate giant cells as a common feature. Among these entities, some are confined to the head and neck region (e.g., central giant cell granuloma and mimicking lesions, i.e., peripheral giant cell granuloma and cherubism) or show a relative predilection for this region (e.g., aneurysmal bone cyst and brown tumor of hyperparathyroidism), while others are rare but associated with distinct underlying disease (e.g., giant cell tumor of bone) or histology (e.g., tenosynovial giant cell tumor of the temporomandibular joint and phosphaturic mesenchymal tumor of the jaws) when occurring in the head and neck. Collectively, these lesions pose great challenge in the pathologic diagnosis, which often requires combinatory assessment from the clinical, histopathologic, and/or molecular aspects. This review provides a summary of pertinent clinical and pathologic features and an update of recent molecular and genetic findings of these entities. The considerations in differential diagnosis as well as the effects of the emerging therapeutic RANKL-antagonizing antibody denosumab will also be addressed.

Molecular Profiling of Atypical Tenosynovial Giant Cell Tumors Reveals Novel Non-CSF1 Fusions

Tenosynovial giant cell tumor (TGCT) is a benign neoplasm characterized by recurrent fusions involving the colony-stimulating factor 1 (CSF1) gene and translocation partners including collagen type VI alpha 3 chain (COL6A3) or S100 calcium-binding protein A10 (S100A10). Herein, we report three atypical TGCT cases with very unusual morphology comprising areas with increased cellular atypia, mitotic activity, and worrisome features that harbor unique non-CSF1 gene fusions. Anchored multiplex PCR (AMP) for next-generation sequencing utilizing a customized panel targeting 86 cancer-related genes was performed, and it identified novel non-CSF1-driven gene fusions: NIPBL-ERG, FN1-ROS1, and YAP1-MAML2. Screening of three control TGCTs with conventional morphology found translocations involving CSF1, with partner genes COL6A3, FN1, and newly identified KCNMA1. All novel fusions were further validated by reverse transcriptase-PCR (RT-PCR) and Sanger sequencing. Late and multiple local recurrences occurred in the atypical TGCTs, while no recurrences were reported in the conventional TGCTs. Our findings reveal that atypical TGCTs harbor gene fusions not implicating CSF1 and suggest that non-CSF1 fusions potentially confer greater propensity to recurrences and local aggressiveness while indicating the presence of alternate pathogenic mechanisms that warrant further investigation.