Clusterin is Expressed in Normal Synoviocytes and in Tenosynovial Giant Cell Tumors of Localized and Diffuse Types: Diagnostic and Histogenetic Implications

Extraaxial Poorly Differentiated Chordoma: Clinicopathologic and Molecular Genetic Characterization

Poorly differentiated chordoma (PDC) is an aggressive subtype of chordoma characterized by SMARCB1 (INI1) loss and a dismal prognosis. It typically involves the axial skeleton, most commonly the skull base and the cervical spine. To our knowledge, only 5 cases of extraaxial PDC (EAPDC) have been reported, and the natural history of these tumors is not fully understood. We studied 6 cases of EAPDC, with the goal of better understanding these exceptionally rare tumors. The tumors occurred in 4 women and 2 men, ranging from 37 to 68 years of age (median, 57.5 years) and involved or originated in the left knee joint (3 cases), right knee joint (2 cases), and right wrist (1 case). Grossly, all were solid and lobulated, with areas of necrosis. Histologically, the tumors were identical to axial PDC, with sheets and lobules of overtly malignant-appearing epithelioid-to-rhabdoid cells with prominent nucleoli. Mitotic activity and necrosis were present. By immunohistochemistry, all cases expressed keratins and brachyury and were SMARCB1 deficient. Molecular genetic analysis identified SMARCB1 loss-of-function alterations in 4 of the tested cases, including mutations (2 cases) and copy number loss (2 cases). DNA methylation profiling of 4 cases of EAPDC showed clustering with axial PDC. Clinical follow-up (6 patients; median, 11.5 months; range, 1-26 months) showed 4 patients to have received transfemoral amputation and 1 extraarticular resection. None received neoadjuvant radiotherapy; 1 received neoadjuvant chemotherapy and 1 adjuvant chemotherapy/immunotherapy. Local recurrences were seen in 2 patients at 7 and 8 months; 3 patients developed metastases 7-11 months after surgery. Two patients were alive with metastatic disease (at 7 and 13 months), 1 died of disease (20 months), and 3 were disease free (1-26 months). We conclude that EAPDC are aggressive malignancies with an unusual predilection for the knee joint and unknown pathogenesis.

Therapeutic advances in Tenosynovial giant cell Tumor: Targeting the CSF1/CSF1R axis

Tenosynovial giant cell tumor is a non-malignant primary locally aggressive articular disease that affects the synovium of joints, tendon sheaths, and bursae. It is characterized by a translocation t (1;2), leading to the overexpression of CSF1 in the tumor microenvironment. CSF1 induces the recruitment of non-malignant cells, mainly macrophages, followed by the differentiation and polarization of these cells into the M2 phenotype. Surgery, particularly total synovectomy, remains the cornerstone of TGCT management. However, recurrence rates vary, reaching 40 to 60% in diffuse disease, often resulting in progressive joint dysfunction, pain, and potential need for joint replacement or limb amputation. Systemic therapy is recommended in recurrent TGCT in patients not amenable to additional surgery. Targeting the CSF1/CSF1R axis has successfully improved tumor responses and enhanced symptomatic function. In this review, we aim to explore contemporary paradigms in inoperable TGCT patients, with a focus on the physiopathology, clinical efficacy, and safety of CSF1 or CSF1R inhibitors.

Diagnostic Challenge of Localized Tenosynovial Giant Cell Tumor in Children

This report describes a rare case of a pediatric tenosynovial giant cell tumor (TSGCT) with a delayed diagnosis. A 9-year-old boy presented with a 3-month history of knee pain and swelling, initially attributed to a femoral non-ossifying fibroma and arthritis based on computed tomography findings and slightly elevated C-reactive protein levels. The symptoms persisted despite medical treatment. Magnetic resonance imaging (MRI) revealed a tumor in the posterior compartment. He underwent surgery, and the pathology confirmed the diagnosis of localized TSGCT. Six months postoperatively, the patient remained asymptomatic. Pediatric knee pain is a complex symptom associated with inflammatory conditions and benign and malignant tumors. Benign tumors, as in this case, can be misdiagnosed as arthritis, delaying diagnosis and treatment. MRI is recommended in cases involving symptom persistence. However, histopathological, immunohistochemical, and morphological examinations are crucial for definitive diagnosis, particularly when the imaging findings are inconclusive.

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.

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.

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

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

Giant Cell Tumor of Soft Tissue: An Updated Review

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

[Localized tenosynovial giant cell tumor : Results from the Histopathological Arthritis Register of the German Society for Orthopedic Rheumatology]

BACKGROUND

The tenosynovial giant cell tumor (pigmented villonodular synovitis) is a proliferative, mainly benign soft tissue tumor of the tendon sheaths, bursae and joints arising from the synovia. It can be divided into circumscribed localized and destructive diffuse types. Approximately 1% of all joint diseases are due to this entity. The tumor is considered as a rarity. Mostly case studies exist. For this study the focus was set on the localized type (L-TSRZT), which accounts for 90% of the diagnoses of this tumor. Given its rarity, data are limited. Therefore, the research aim was to provide data on prevalence, primary location and sensitivity of clinical versus histopathological diagnosis in a German sample.

METHODS

Based on the Histopathological Arthritis Register of the German Society for Orthopedic Rheumatology, the data of the L‑TSRZT were retrospectively analyzed (time frame 1 January 2018-28 December 2020).

RESULTS

This database contained N = 7595 cases of arthropathy. A total of n = 45 patients with the diagnosis L‑TSRZT were identified. The prevalence of the tumor was 0.6%, 95% CI [0.4%, 0.8%], or 5.9 cases per 1000. The primary location involved the finger (48.9%). In 14 of 45 cases the diagnosis was correctly determined from the clinical side, corresponding to a sensitivity of 31.1%, 95% CI [18.2%, 46.7%].

CONCLUSION

For the first time, this paper was able to provide data on a large sample for Germany. Notably, the low sensitivity of the clinical diagnosis confirms the importance of histopathology for diagnosing L‑TSRZT.

Myxoinflammatory Fibroblastic Sarcoma

MIFS is a low-grade fibroblastic sarcoma that predilects to superficial distal extremity soft tissue. It is composed of plump spindled and epithelioid cells, inflammatory infiltrates, and mucin deposits in a fibrosclerotic stroma. Large epithelioid cells harboring bizarre nuclei and virocyte-like macronucleoli and pleomorphic pseudolipoblasts are characteristic. While conventional MIFS has locally recurrent potential but minimal metastatic risk, tumors with high-grade histologic features have a greater risk for recurrence and metastasis. Wide local excision is the recommended treatment.

Localized tenosynovial giant cell tumor in children

Background

To investigate the clinical characteristics and surgical efficacy of localized tenosynovial giant cell tumors in children.

Methods

The clinical data, surgery, and follow-up results of 17 children with localized tenosynovial giant cell tumors who visited our hospital from 2011 to 2021 were collected for statistical analysis.

Results

The median patient age was 7 years and 8 months, and the ratio of males to females was 1.43 (10/7). The predilection of disease was similar in hands and feet, and the common presenting symptom was mass. One patient experienced recurrence after surgery, and one child had postoperative functional limitations.

Conclusion

Extremities are common sites of localized tenosynovial giant cell tumors in children. Complete surgical resection helps reduce the recurrence rate.

Level of evidence

Level III.

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.

Interactions in CSF1-Driven Tenosynovial Giant Cell Tumors

PURPOSE

A major component of cells in tenosynovial giant cell tumor (TGCT) consists of bystander macrophages responding to CSF1 that is overproduced by a small number of neoplastic cells with a chromosomal translocation involving the CSF1 gene. An autocrine loop was postulated where the neoplastic cells would be stimulated through CSF1R expressed on their surface. Here, we use single-cell RNA sequencing (scRNA-seq) to investigate cellular interactions in TGCT.

EXPERIMENTAL DESIGN

A total of 18,788 single cells from three TGCT and two giant cell tumor of bone (GCTB) samples underwent scRNA-seq. The three TGCTs were additionally analyzed using long-read RNA sequencing. Immunofluorescence and IHC for a range of markers were used to validate and extend the scRNA-seq findings.

RESULTS

Two recurrent neoplastic cell populations were identified in TGCT that are highly similar to nonneoplastic synoviocytes. We identified GFPT2 as a marker that highlights the neoplastic cells in TCGT. We show that the neoplastic cells themselves do not express CSF1R. We identified overlapping MAB features between the giant cells in TGCT and GCTB.

CONCLUSIONS

The neoplastic cells in TGCT are highly similar to nonneoplastic synoviocytes. The lack of CSF1R on the neoplastic cells indicates they may be unaffected by current therapies. High expression of GFPT2 in the neoplastic cells is associated with activation of the YAP1/TAZ pathway. In addition, we identified expression of the platelet-derived growth factor receptor in the neoplastic cells. These findings suggest two additional pathways to target in this tumor.

Diffuse-Type Tenosynovial Giant Cell Tumour Involving Bone Masquerading as Langerhans Cell Histiocytosis

We presented a case of diffuse-type tenosynovial giant cell tumour (DTSGCT) of foot masquerading as Langerhans cell histiocytosis. Preliminary diagnosis by needle biopsy was difficult due to the major involvement of bones and the overshadowing effect of the accompanying Langerhans cells. The complete curettage specimen with relevant immunohistochemistry and molecular tests made the final diagnosis of DTSGCT possible. The biomolecular mechanism for the masquerading phenomenon was explained by CSF1 overexpression in the neoplastic cells attracting migration and proliferation of CSF1R-positive Langerhans cells.

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.

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.

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.

[Joint tumors: rare but important differential diagnoses of malignant and benign tumors as well as pseudotumors in rheumatology]

This review article elucidates the differential diagnostics of malignant and benign joint tumors, pseudotumors of the joints and the peri-implant tissue, which are rare but important entities in rheumatology and orthopedic rheumatology. The tissue of origin includes the synovium, peri-implant tissue, peri-articular fibrous tissue and peri-articular osseous tissue. Pseudotumors can be viewed as independent but heterogeneous entities. These are essentially manifested as tumor-like depositions of crystals, calcareous deposits, vascular malformations, ectasia of the synovia and joint capsule tissue and pseudocysts. Other causes for pseudotumors are focal destructive inflammation (e.g. induced by foreign bodies), high grade synovitis and focal fibrinoid necrosis (i.e. rheumatoid nodules). Methodologically, these diagnostics are based on conventional standard staining methods, immunohistochemical analyses of formalin-fixed and paraffin-embedded materials and on molecular diagnostic procedures. The latter are of great importance in cases of benign and malignant joint tumors. The most important immunohistochemical markers with respect to joint tumors are S100, SM-actin, CD68, CD34, STAT6, clusterin, Muc‑4, beta-catenin and MDM2-FISH. The following markers are recommended for the differential diagnostics and typing of periarticular tumor metastases in the pathology of rheumatic diseases: AE1/AE3, CK8, p63, TTF‑1, TGB, PSA, androgen receptor, GATA, CD56, chromogranin, CDX‑2, SAT-B2, SALL4, estrogen and progesterone receptors, CD45LCA, CD30, CD79a and S100. Necrosis, inflammatory infiltrations and reparative inflammatory changes may complicate the histopathological classification. Therefore, a correlation with clinical, microbiological and radiological data in the sense of interdisciplinary synergistic diagnostics may be required.

Tenosynovial Giant Cell Tumor of the Retropharynx: A Case Report With Literature Review

Tenosynovial giant cell tumor (TSGCT) represents a family of benign tumors that arise from the synovial tissue of a joint, tendon sheath, or bursa. It usually involves the joints of the extremities and rarely occurs in the head and neck region. Here, we describe a case of a 32-year-old man with a submucosal mass bulging in the posterior pharyngeal wall since one month. The lesion was removed and diagnosed with localized type of TSGCT based on histopathological investigations and clinical presentation. It is very rare that TSGCT occurs in the retropharynx, which reminds clinicians to consider this entity as a possible diagnosis.

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.

Tenosynovial Giant Cell Tumor, Localized Type With Extensive Chondroid Metaplasia: A Case Report With Immunohistochemical and Molecular Genetic Analysis

Tenosynovial giant cell tumor (TSGCT) of localized type is a common disease occurring mostly in the hands. Diagnosis of this tumor is relatively easy to render with hematoxylin-eosin-stained sections as compared with that of TSGCT of diffuse type. However, very rare cases with chondroid metaplasia that have recently been reported mainly in diffuse type can make pathological differentiation from soft tissue cartilaginous tumors extremely difficult. In this article, the authors present the second reported case of TSGCT of localized type showing extensive chondroid metaplasia. Pathological interpretation was difficult without utilizing immunohistochemistry and fluorescence in situ hybridization. One must be careful not to misdiagnose this lesion as cartilaginous tumors of soft tissue, and we suspect at least some chondroblastoma-like chondroma could be reclassified as TSGCT of localized type with extensive chondroid metaplasia. Morphological, immunohistochemical, and molecular genetic characteristics are presented and discussed.

Histiocyte-rich rhabdomyoblastic tumor: rhabdomyosarcoma, rhabdomyoma, or rhabdomyoblastic tumor of uncertain malignant potential? A histologically distinctive rhabdomyoblastic tumor in search of a place in the classification of skeletal muscle neoplasms

Skeletal muscle tumors are traditionally classified as rhabdomyoma or rhabdomyosarcoma. We have identified an unusual adult rhabdomyoblastic tumor not clearly corresponding to a previously described variant of rhabdomyoma or rhabdomyosarcoma, characterized by a very striking proliferation of non-neoplastic histiocytes, obscuring the underlying tumor. Ten cases were identified in nine males and one female with a median age of 43 years (range 23-69 years). Tumors involved the deep soft tissues of the trunk (N = 4), lower limbs (N = 4), and neck (N = 2). Tumors were well-circumscribed, nodular masses, frequently surrounded by a fibrous capsule containing lymphoid aggregates and sometimes calcifications. Numerous foamy macrophages, multinucleated Touton-type giant cells, and sheets/fascicles of smaller, often spindled macrophages largely obscured the underlying desmin, MyoD1, and myogenin-positive rhabdomyoblastic tumor. Cases were wild type for MYOD1 and no other mutations or rearrangements characteristic of a known subtype of rhabdomyoma or rhabdomyosarcoma were identified. Two of four cases successfully analyzed using a next-generation sequencing panel of 170 common cancer-related genes harbored inactivating NF1 mutations. Next-generation sequencing showed no gene fusions. Clinical follow (nine patients; median 9 months; mean 23 months; range 3-124 months) showed all patients received wide excision; four patients also received adjuvant radiotherapy and none received chemotherapy. At the time of last follow-up, all patients were alive and without disease; no local recurrences or distant metastases occurred. We hypothesize that these unusual tumors represent rhabdomyoblastic tumors of uncertain malignant potential. Possibly over time they should be relegated to a new category of skeletal muscle tumors of intermediate (borderline) malignancy.

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

We present our experience with ten well-characterized malignant tenosynovial giant cell tumors, including detailed immunohistochemical analysis of all cases and molecular cytogenetic study for CSF1 rearrangement in a subset. Cases occurred in 7 M and 3 F (mean age: 52 years; range: 26-72 years), and involved the ankle/foot (n = 1), finger/toe (n = 3), wrist (n = 1), pelvic region (n = 3), leg (n = 1), and thigh (n = 1). There were eight primary and two secondary malignant tenosynovial giant cell tumors. Histologically, all cases showed definite areas of typical tenosynovial giant cell tumor. The malignant areas varied in appearance. In some cases, isolated malignant-appearing large mononuclear cells with high nuclear grade and mitotic activity were identified within otherwise-typical tenosynovial giant cell tumor, as well as forming larger masses of similar-appearing malignant cells. Occasionally, these nodules of malignant large mononuclear cells showed transition to pleomorphic spindle cell sarcoma, with varying degrees of collagenization and myxoid change. One malignant tenosynovial giant cell tumor was composed of sheets of monotonous large mononuclear cells with high nuclear grade, growing in a hyalinized, osteoid-like matrix, with areas of heterologous osteocartilaginous differentiation. Mitotic activity ranged from 2 to 34 mitoses per 10 HPF (mean 18/10 HPF). Geographic necrosis was observed in four cases. The malignant-appearing large mononuclear cells were consistently positive for clusterin and negative for CD163, CD68, and CD11c. Desmin was positive in a small minority of these cells. Areas in malignant tenosynovial giant cell tumor resembling pleomorphic spindle cell sarcoma or osteo/chondrosarcoma showed loss of clusterin expression. RANKL immunohistochemistry was positive in the large mononuclear cells in eight cases. Two cases showed an unbalanced rearrangement of the CSF1 locus. Follow-up (nine patients; range 0.5-66 months; mean 20 months) showed three patients dead of disease, with three other living patients having lung and lymph node metastases; three patients were disease-free. We conclude that malignant tenosynovial giant cell tumors are highly aggressive sarcomas with significant potential for locally destructive growth, distant metastases, and death from disease. The morphologic and immunohistochemical features of these tumors and the presence of CSF1 rearrangements support origin of malignant tenosynovial giant cell tumor from synoviocytes.

Diffuse Tenosynovial Giant Cell Tumor Around the Temporomandibular Joint: An Entity With Special Radiologic and Pathologic Features

PURPOSE

Diffuse tenosynovial giant cell tumor (TGCT) of the temporomandibular joint (TMJ) is rare. The aim of the present study was to summarize the clinical, radiologic, and pathologic features of this tumor.

MATERIALS AND METHODS

Nine cases of TGCT in the TMJ region were examined. All available radiologic and pathologic documents were carefully reviewed. These cases were grouped into 3 types according to the radiologic features: bone-centered type, intraosseous type, and soft tissue type. Cases reported in the literature were reviewed to better summarize the clinical characteristics.

RESULTS

TGCTs in the TMJ region showed some special radiologic and pathologic features. Radiologically, the lesion could be centered in the craniofacial bone or centered in the surrounding soft tissue. Four cases were categorized as the bone-centered type, 1 was categorized as the intraosseous type, and 4 were categorized as the soft tissue type. Pathologically, epithelioid mononuclear cells with abundant eosinophilic cytoplasm and eccentric nuclei were observed in all cases. Chondroid metaplasia was noted in 8 cases. Some areas were similar to giant cell reparative granuloma and chondroblastoma. All patients who underwent complete tumor resection showed no evidence of recurrence at follow-up. Of the 93 reported cases, only 5 developed postoperative recurrence and distant metastasis.

CONCLUSION

TGCTs of the TMJ region share similar radiologic and pathologic features as other tumors, which indicates the TGCT might be a special entity within a spectrum of diseases.

Chondroid Tenosynovial Giant Cell Tumor of the Temporomandibular Joint: A Rare Case Report

Tenosynovial giant cell tumor of diffuse type (TGCT-d) or pigmented villonodular synovitis (PVNS) is a locally aggressive lesion that mostly affects the joints of long bones. Chondroid tenosynovial giant cell tumor (CTGCT) or PVNS with chondroid metaplasia is a rare distinct subset of synovial tumors that has a predilection for the TMJ. We report a rare case of CTGCT in the TMJ, initially misdiagnosed as temporomandibular disorder (TMD). A 51-year-old woman was referred to the surgeon with the chief complaint of TMJ pain for 5 years and a past history of an unsuccessful TMD treatment. Extraoral examination revealed discrete preauricular swelling and restricted mandibular range of motion. Panoramic radiograph and computerized tomography showed destruction of the mandibular fossa and condyle. Histologically, the tumor was composed by large mononuclear cells with prominent eosinophilic cytoplasm and grooved nuclei, small histiocytoid cells, osteoclast-like multinucleated cells, brown pigmentation and areas of chondroid metaplasia. Morphological and immunohistochemical characteristics lead to the final diagnosis of CTGCT. The rarity of CTGCT could be attributed to the lack of recognition of this lesion, with cases diagnosed as chondroblastomas, synovial chodromatosis and chondrosarcoma. The patient received immediate reconstruction and recurrence was found 22 months after initial intervention. TGCT-d and CTGCT of the TMJ can present similar symptoms to TMD, but clinicians must distinguish both lesions by complete examination, imaging and, when necessary, histopathologic evaluation.

Selected Giant Cell Rich Lesions of the Temporal Bone

Giant cell rich lesions of the temporal bone encompass a wide spectrum of disease that includes infectious, reactive, and neoplastic processes. When dealing with any lesion that can potentially involve bone, it is important to understand both the clinical presentation and to correlate the histologic findings with the radiologic imaging. This review discusses the clinical, the pathologic features including the differential diagnosis, and the treatment of some of the more commonly encountered giant cell rich entities in this region.

Clusterin in Neuroendocrine Epithelial Neoplasms: Absence of Expression in a Well-differentiated Tumor Suggests a Jejunoileal Origin

Clusterin, a widely expressed, tissue-specific glycoprotein, is a diagnostic marker of several tumor types, including anaplastic large cell lymphoma, follicular dendritic cell sarcoma, and tenosynovial giant cell tumor. A recent study has suggested it is highly expressed by well-differentiated neuroendocrine tumors (NET) arising at most anatomic sites, with the exception of jejunoileal tumors, and that it is similarly not expressed by poorly differentiated neuroendocrine carcinomas (NEC). We sought to validate this result in a large cohort of NETs and NECs. Clusterin immunohistochemistry was performed on tissue microarrays of 255 NETs [45 lung, 4 stomach, 8 duodenum, 75 pancreas (62 primary, 13 metastatic), 107 jejunoileum (69 primary, 38 metastatic), 16 appendix] and 88 NECs (43 visceral, 45 Merkel cell). Extent (%) and intensity (0, 1+, 2+, 3+) of staining were assessed and an H-score (extent x intensity) calculated. An average H-score >5 was considered positive. Clusterin expression was noted in 82.4% of 148 nonjejunoileal NETs (average H-score 183) and only 8.4% of 107 jejunoileal NETs (average H-score, 31), as well as 19.3% of NECs (average H-score, 36). Clusterin is frequently, strongly expressed by NETs of diverse anatomic sites, with the exception of jejunoileal tumors, in which it is only rarely, weakly expressed. It is occasionally, weakly expressed by NECs. Most metastatic NETs of occult origin arise in the pancreas or the jejunoileum. For cases in which an initial site of origin immunopanel (eg, islet 1, PAX6, CDX2) is ambiguous, addition of clusterin may be diagnostically useful, with absence of expression suggesting a jejunoileal origin.

Selected Lesions Featuring Giant Cells

Many neoplasms of the soft tissues feature giant cells, but this article covers entities in which giant cells are a striking feature. Specifically, we consider tenosynovial giant cell tumor (localized and diffuse types; giant cell tumor of tendon sheath, and pigmented villonodular tenosynovitis), reticulohistiocytoma, juvenile xanthogranuloma, giant cell fibroblastoma (a variant form of dermatofibrosarcoma protuberans), giant cell angiofibroma (which is essentially a giant cell-rich form of solitary fibrous tumor), and phosphaturic mesenchymal tumor.

Multiple metastases from histologically benign intraarticular diffuse-type tenosynovial giant cell tumor: a case report

Diffuse-type tenosynovial giant cell tumor (D-TGCT) is a relatively rare mesenchymal tumor. It is a locally aggressive but virtually nonmetastasizing neoplasm and thus regarded as benign. Only a few D-TGCTs with benign histology have been reported to metastasize. We report an extremely rare case of benign D-TGCT in which multiple metastases developed 9 years after surgery for the primary tumor. The present case suggests that conventional D-TGCT has the potential to form distant metastases, albeit exceptionally rarely, and that this probable implantation phenomenon can be managed conservatively.

Hepatoid tenosynovial giant cell tumor - a rare morphologic variant case report

We report a morphologically rare type of tenosynovial giant cell tumor (TSGCT), localized type, occurring in a 49-year-old man. Imaging examination revealed multiple nodular lesions around the right knee joint. The largest one extended to both intra- and extra-osseous region of the right distal femur. Histologically, the tumor consisted of epithelioid mononuclear cells and they looked like to have abundant eosinophilic cytoplasm reminiscent of hepatic tissues. In some areas, however, typical histologic features of TSGCT were observed. Electron microscopy revealed that the eosinophilic cytoplasm-like substance was intercellular fibrinous material surrounding the mononuclear tumor cells. Immunohistochemically, mononuclear tumor cells and multinucleate giant cells were positive for CD68 (Kp1) and some of the mononuclear tumor cells were also positive for desmin. Finally, we made the diagnosis of hepatoid TSGCT.

Cytologic findings from a benign giant cell tumor of the tendon sheath in a dog

A 6-year-old male neutered Australian Shepherd dog was presented for evaluation of a subcutaneous mass on the plantar aspect of the proximal left metatarsus. Fine-needle aspirate smears contained numerous plump spindle cells and large multinucleated cells amongst a considerable amount of pink extracellular matrix. Histopathologic diagnosis of the tissue obtained during initial biopsy and eventual surgical cytoreduction of the mass was a benign giant cell tumor of the tendon sheath (GCTTS). Immunohistochemically, the synovioblastic neoplastic cells were diffusely strongly positive for vimentin and S-100, were multifocally moderately positive for cytokeratin AE1/3, and were negative for CD18, muscle-specific actin (MSA), and melanoma-associated antigen (mutated) 1 (MUM-1). The dog recovered from surgery and underwent definitive radiation therapy to treat the local residual disease. Eight months later, the mass had not recurred. The diagnosis of GCTTS in this case supports previously published reports describing GCTTS as a relevant disease entity in dogs, and provides the first documentation of cytologic findings with this tumor. Further investigation is needed to correlate pathologic features with clinical behavior and response to therapy in dogs.

Myxoinflammatory fibroblastic sarcoma: a clinicopathologic analysis of 104 cases, with emphasis on predictors of outcome

In this study, we examine the clinicopathologic features of 104 cases of myxoinflammatory fibroblastic sarcoma (MIFS), a low-grade, inflammatory fibromyxoid tumor with a predilection to distal extremity soft tissue, and attempt to identify factors predictive of aggressive behavior. The study cohort consisted of 49 male and 55 female patients ranging in age from 17 to 83 (mean, 42; median, 39) years. The tumor arose primarily on the dorsal aspect of the distal extremities as a solitary and usually painless mass. Tumors ranged in size from 0.5 to 15 (mean, 3.2; median; 2.4) cm. Microscopically, tumors consisted of variably cellular and inflamed fibromyxoid tissue growing as a lobulated mass or as multiple nodules within subcutaneous tissue or along tendinofascial planes. Tumor cells ranged from plump spindled to more epithelioid cells with enlarged, vesicular nuclei. Characteristic of the process was a strikingly bizarre cell with an inclusion body-like nucleolus (85% of cases) and/or a smudgy hyperchromatic nucleus (51%) present in all but 7 cases. The mitotic rate per 50 high-power field ranged from 0 to 13 (mean, 2,9; median, 2) mitoses. Twenty-two tumors demonstrated 1 or more of the following atypical features: (1) foci with complex sarcoma-like vasculature; (2) hypercellular areas; and (3) increased mitotic activity or atypical mitotic figures. Immunohistochemically, tumor cells demonstrated immunoreactivity for vimentin (100%), D2-40 (86%), CD34 (50%), keratin(s) (33%), CD68 (27%), actin(s) (26%), desmin (9%), S-100 protein (7%), and epithelial membrane antigen (6%). Thirty of 59 patients (51%) with follow-up data suffered (at least) 1 local recurrence, and 1 patient developed metastatic disease after multiple local recurrences. Completeness of initial surgical excision was the only clinicopathologic parameter that statistically correlated with a lower incidence of recurrence (P=0.004). Histologically atypical MIFS recurred more often than conventional tumors (67% vs. 47%), but the difference was not statistically significant (P=0.35). Our study shows that histologic features often associated with more aggressive sarcomas do not substantially impact the morbidity of MIFS, and complete surgical excision provides the best chance for disease-free survival.

Podoplanin and clusterin are reliable markers of nonneoplastic synovium at various sites

INTRODUCTION

Clusterin (CLU) has been noted to mark synovium adjacent to tenosynovial tumors, and studies suggest that podoplanin (PP) is upregulated in inflammatory arthritis. Characterization of synovial staining with CLU and PP in various nonneoplastic disease states has not been described.

METHODS

A microarray was created from paraffin-embedded human synovium, including 19 normal/noninflammatory (10 weight-bearing joints, 8 non-weight-bearing joints), 9 rheumatoid arthritis, 10 synovial cysts, and 3 osteoarthritis and stained with PP (D2-40) and CLU. Staining intensity was graded semiquantitatively (0-3+).

RESULTS

PP and CLU stained synovium in 88% and 95% cases, respectively. PP and CLU showed moderate to strong (3+) staining in 26% and 19% of noninflammatory and 44% and 0% of inflammatory synovia, respectively (P < .01).

CONCLUSIONS

PP and CLU are reliable markers of human synovium and can confirm its presence in limited specimens. Although CLU was more sensitive, PP may be more useful in the setting of chronic inflammation.

Fibrohistiocytic tumors and related neoplasms in children and adolescents

Fibrohistiocytic tumors (FHTs) in children and adolescents range from the benign fibrous histiocytoma, or dermatofibroma, to a variety of intermediate and malignant neoplasms, such as dermatofibrosarcoma protruberans and high-grade undifferentiated pleomorphic sarcoma (malignant fibrous histiocytoma). Those tumors as a group are comprised of fibroblasts, myofibroblasts, and histiocytes-dendritic cells with a variably prominent inflammatory infiltrate consisting of lymphocytes and eosinophils. Dendritic cells are also a major constituent of another group of neoplasms that include Langerhans cell histiocytosis, follicular and interdigitating cell sarcomas, and juvenile xanthogranuloma. These latter tumors are considered in this discussion for the sake of differential diagnosis and their possible histogenetic relationship to FHTs. Recent studies have suggested that the relationship between the fibroblast and histiocyte in the FHTs may reflect the intrinsic capacity to transdifferentiate from one to the other morphologic and functional state. The so-called "facultative fibroblast," as a cell with fibroblastic and histiocytic properties, was discussed in the context of the fibrous xanthoma 50 years ago. Possibly the entire histogenetic concept of FHTs should be reconsidered in light of current studies.

Tumors and diseases of the joint

A variety of different diseases affect the synovium, including infection, noninfectious immunologic inflammatory conditions, degenerative arthroses, crystal deposits, trauma, and tumors. Tumors of the synovium are relatively uncommon. Any mesenchymal tumor may arise in the synovium, but most recapitulate its normal counterpart including synoviocytes, blood vessels, fat, and fibrous tissue. These tumors can arise in any synovial lined structures both within joints and in extraarticular locations. Most synovial tumors are benign. Malignant tumors are rare but important to recognize because many are aggressive and must be treated appropriately. Among common nonneoplastic conditions that affect the synovium and surrounding structures are crystal deposits such as monosodium urate crystals, calcium pyrophosphate dihydrate crystals, and hydroxyapatite crystals. These crystal deposits may be asymptomatic or cause severe pain or chronic joint destruction. Their accurate identification is important to guide appropriate therapy.

Chondroid tenosynovial giant cell tumor: a clinicopathological and immunohistochemical analysis of 5 new cases

Tenosynovial giant cell tumor (TGCT) arises from the synovium of joints or tendon sheaths. Chondroid metaplasia in TGCT is rare with only 4 well-documented cases reported in the literature. The authors describe the morphological features and immunophenotype of 5 new cases of chondroid TGCT emphasizing a broader range of matrix patterns in these tumors and an expanded immunophenotype, specifically, staining for clusterin and podoplanin which have recently been found to be expressed in conventional TGCTs. Chondroid metaplasia was extensive in 3 cases. Matrix patterns included chondromyxoid, chondro-osseous, hyaline-like, and lace-like calcification similar to that seen in chondroblastoma. The authors conclude that chondroid TGCT is a rare, distinct synovial tumor with a predilection for the temporomandibular joint that has a similar immunophenotype as conventional TGCT. Chondroid metaplasia may be extensive and have a variety of matrix patterns. Chondroid TGCT needs to be distinguished from other chondroid lesions, including chondroblastoma and chondrosarcoma.

Macrophages in Langerhans cell histiocytosis are differentiated toward M2 phenotype: their possible involvement in pathological processes

Although numerous macrophages are found in the lesions of Langerhans cell histiocytosis (LCH), their activation phenotypes and their roles in the disease process have not been clarified. Paraffin-embedded LCH samples were examined on immunohistochemistry and it was found that CD163 can be used to distinguish infiltrated macrophages from neoplastic Langerhans cells (LC). The number of CD163-positve macrophages was positively correlated with the number of multinucleated giant cells (MGC), indicating that most MGC are derived from infiltrated macrophages. A significant number of CD163-positive macrophages were positive for interleukin (IL)-10 and phospho-signal transducer and activator of transcription-3 (pSTAT3), an IL-10-induced signal transduction molecule. This indicates that these macrophages are polarized to anti-inflammatory macrophages of M2 phenotype. Tumor-derived macrophage-colony-stimulating factor (M-CSF) was considered to responsible for inducing M2 differentiation of infiltrated macrophages. The number of CD163-positive macrophages in different cases of LCH varied, and interestingly the density of CD163-positive macrophages was inversely correlated with the Ki-67-positivity of LC. Although the underlying mechanism is not fully elucidated, macrophage-derived IL-10 was considered to be involved in the suppression of tumor cell proliferation via activation of STAT3.