Primary synovial sarcoma of bone: A retrospective analysis of 25 patients

Comment on Manole et al. Primary Pericardial Synovial Sarcoma: A Case Report and Literature Review. Diagnostics 2022, 12, 158

With great interest, we read the article by Manole et al [...].

Case report: Characteristics and nature of primary cardiac synovial sarcoma

Primary malignant cardiac tumors rarely occur, and cardiac synovial sarcoma (SS) is especially rare among such tumors. Herein, we present the case of a 35-year-old female with primary cardiac SS treated with surgery, chemotherapy, and radiotherapy. She presented with chest symptoms and underwent imaging examinations. A cardiac tumor was suspected, and an open biopsy was performed. The pathological findings suggested cardiac SS. Next, we performed a resection, and the tumors persisted at a macroscopic level. Immunohistochemistry was negative for SS18-SSX and positive for the SSX C-terminus and cytokeratin CAM5.2, a reduction of SMARCB1/INI1 was observed, and fluorescence in situ hybridization showed positive SS18 split staining. Owing to the FNCLCC grade 3 tumor and R2 margins, adjuvant chemotherapy with ifosfamide, doxorubicin, and radiotherapy was initiated, and the patient was diagnosed with cardiac SS. The differences in patients with cardiac SS compared with general SS include male predominance, larger tumor size, and poorer prognosis. Pathological findings of immunohistochemistry and fluorescence in situ hybridization were found to be more reliable than imaging findings for a correct diagnosis. Additionally, because incomplete resection is frequently performed, adjuvant therapy, including chemotherapy and radiation therapy, may be performed. The findings indicate that multiple therapies, including surgery, chemotherapy, and radiotherapy, are essential treatment strategies for improving the prognosis of patients with cardiac SS.

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.

Kinase fusion positive intra-osseous spindle cell tumors: A series of eight cases with review of the literature

Mesenchymal spindle cell tumors with kinase fusions, often presenting in superficial or deep soft tissue locations, may rarely occur in bone. Herein, we describe the clinicopathologic and molecular data of eight bone tumors characterized by various kinase fusions from our files and incorporate the findings with the previously reported seven cases, mainly as single case reports. In the current series all but one of the patients were young children or teenagers, with an age range from newborn to 59 years (mean 19 years). Most tumors (n = 5) presented in the head and neck area (skull base, mastoid, maxilla, and mandible), and remaining three in the tibia, pelvic bone, and chest wall. The fusions included NTRK1 (n = 3), RET (n = 2), NTRK3 (n = 2), and BRAF (n = 1). In the combined series (n = 15), most tumors (73%) occurred in children and young adults (<30 years) and showed a predilection for jaw and skull bones (40%), followed by long and small tubular bones (33%). The fusions spanned a large spectrum of kinase genes, including in descending order NTRK3 (n = 6), NTRK1 (n = 4), RET (n = 2), BRAF (n = 2), and RAF1 (n = 1). All fusions confirmed by targeted RNA sequencing were in-frame and retained the kinase domain within the fusion oncoprotein. Similar to the soft tissue counterparts, most NTRK3-positive bone tumors in this series showed high-grade morphology (5/6), whereas the majority of NTRK1 tumors were low-grade (3/4). Notably, all four tumors presenting in the elderly were high-grade spindle cell sarcomas, with adult fibrosarcoma (FS)-like, malignant peripheral nerve sheath tumor (MPNST)-like and MPNST phenotypes. Overall, 10 tumors had high-grade morphology, ranging from infantile and adult-types FS, MPNST-like, and MPNST, whereas five showed benign/low-grade histology (MPNST-like and myxoma-like). Immunohistochemically (IHC), S100 and CD34 positivity was noted in 57% and 50%, respectively, while co-expression of S100 and CD34 in 43% of cases. One-third of tumors (4 high grade and the myxoma-like) were negative for both S100 and CD34. IHC for Pan-TRK was positive in all eight NTRK-fusion positive tumors tested and negative in two tumors with other kinase fusions. Clinical follow-up was too limited to allow general conclusions.

Spectrum of Histopathological, Immunohistochemical, Molecular and Radiological Features in 12 Cases of BCOR::CCNB3-positive Sarcomas With Literature Review

Introduction BCOR::CCNB3-positive undifferentiated sarcomas are rare. Herein, we present clinicopathological features including immunohistochemical and molecular data, along with the radiological profile of 12 such tumors. Methods Tumors were tested for BCOR::CCNB3 fusion by reverse transcription polymerase chain reaction (RT-PCR) technique. Eight tumors were tested for EWSR1 and three for SS18 gene rearrangements by fluorescence in situ hybridization, and two for SS18::SSX fusion by fragment analysis. Results Ten of 12 patients were male with ages ranging between 4 and 17 years (median = 13, average = 14.4). Nine tumors occurred in bones and three in soft tissues (median size = 8 cm). Four of five tumors within the appendicular bones were metadiaphyseal and appeared as permeative lesions, invariably associated with cortical thickening. Three tumors displayed mineralization. Histopathologically, the tumors comprised round to epithelioid cells with round to oval to spindle-shaped nuclei, mostly diffusely arranged in a myxoid stroma with intervening thin-walled vessels. Immunohistochemically, tumor cells were positive for BCOR (10/11), SATB2 (8/9), TLE1 (5/6), cyclinD1 (4/4), and EMA (3/8). All tumors revealed BCOR::CCNB3 fusion transcript. Nine patients underwent neoadjuvant chemotherapy, including five who underwent surgical resection, with two patients, who received adjuvant radiation therapy. A single patient, each, underwent palliative chemotherapy and palliative radiotherapy, respectively. Four patients developed pulmonary metastasis and three developed local recurrences. Four patients were alive-with-disease and two were free-of-disease. Conclusions It is crucial to identify BCOR::CCNB3 fusion-positive sarcomas, given significant treatment-associated implications. Certain clinicoradiological, histopathological features, absent EWSR1 rearrangement and BCOR, SATB2, and TLE1 immunoexpression are useful for triaging these tumors for molecular testing. A review of the literature on these ultra-rare tumors, including their diagnostic mimics is presented.

SS18-SSX Antibody: A Useful Tool to Save Time and Reduce Costs in Synovial Sarcoma Diagnosis. Proposal of a Novel Diagnostic Algorithm

Synovial sarcoma is a rare malignant mesenchymal neoplasm mostly affecting young adults, characterized by a specific translocation which results in the fusion of the SS18 gene on chromosome 18 with one of the three highly homologous SSX genes on chromosome X. Its morphological diagnosis, especially in monophasic or poorly differentiated variants, can be challenging because histological features often overlap with other malignant mesenchymal tumors. Until recently, the differential diagnosis mostly relied on the use of cytogenetic or molecular analyses to detect the specific t(X;18)(p11;q11) translocation, thus virtually restricting its correct identification to referral centers with a high histological and molecular pathology workflow. The recently commercialized highly sensitive and fusion-specific SS18-SSX antibody has significantly improved the approach to these tumors, representing a relatively cheap and easy to access tool for synovial sarcoma diagnosis. Through a retrospective analysis of 79 synovial sarcomas and histological mimickers, this study confirms the usefulness of the SS18-SSX antibody in the diagnosis of synovial sarcoma, particularly focusing on its application in the pathological response evaluation after neoadjuvant treatment as well as its time- and cost-saving advantages. Finally, we here propose a new diagnostic algorithm to apply into the routine practice.

Expanding the Use of an SS18-SSX Antibody for Molecular Assays in Synovial Sarcoma

Synovial sarcoma is an aggressive malignancy that generally affects adolescents and young adults and is characterized by high rates of recurrence and metastasis, with a 10-year survival rate of about 50%. The fusion oncoprotein SS18-SSX, the product of a pathognomonic chromosomal translocation t(X;18), is the oncogenic driver of this sarcoma, disrupting differentiation through widespread epigenetic dysregulation. Experimental research into SS18-SSX biology has been limited by the lack of an antibody that specifically detects the endogenous fusion oncoprotein as opposed to its native SS18 or SSX components. Recently, a rabbit monoclonal antibody was developed and made commercially available, which specifically detects the fusion junction site epitope of SS18-SSX as found in at least 95% of synovial sarcomas. Here, we characterize a suite of molecular biology assays using this new antibody, both confirming existing and reporting on novel applications. We demonstrate its high sensitivity and specificity for synovial sarcoma diagnosis on patient samples through positive immunohistochemical staining on synovial sarcoma, tissue microarray, and full face sections. In addition, we demonstrate detection of the human SS18-SSX protein when expressed in a genetically engineered mouse model of synovial sarcoma. We also demonstrate nuclear staining of SS18-SSX in synovial sarcoma cells using immunofluorescence, and visualize the interaction between SS18-SSX and the BAF complex member BRG1 through a proximity ligation assay. Lastly, we confirm the interaction between SS18-SSX and promoter regions of target genes through chromatin immunoprecipitation. This antibody represents a breakthrough in sarcoma research and has value in multiple applications to expand the knowledge of synovial sarcoma biology.