Refer to Pulmonary Synovial Sarcoma for additional details.
Definition
• A mesenchymal spindle cell neoplasm that demonstrates variable epithelial differentiation and possesses a specific chromosomal translocation, t(X;18)(p11;q11), resulting in the fusion of SYT and SSX genes
Clinical features
Epidemiology
• Primary intrathoracic sarcomas are exceedingly rare, and meaningful epidemiological data are difficult to report
• The majority of primary cardiac tumors are benign (most commonly myxoma), but approximately 25% are various sarcoma subtypes
• An incidence between 0.002% and 0.3% has been reported
Presentation
• Clinical symptoms vary with tumor location and are often secondary to obstruction, embolism, and tamponade
• Primary cardiac SS is more commonly seen in the atria and pericardial surfaces
Prognosis and treatment
• SS, intrathoracic and soft tissue, is considered an aggressive tumor; most are seen as grade II (Fédération Nationale des Centres de Lutte Contre le Cancer)
• Similar to SS arising from all locations, the main prognostic factor remains the ability for complete resection, which is often difficult for cardiac tumors
Pathology
Gross
• Morphological features show infiltrative, firm white lesions with variable hemorrhage and necrosis
Histology
• Intrathoracic and extrathoracic SS are histologically identical, displaying two major subtypes, biphasic and monophasic
• Biphasic tumors contain both epithelial and spindle cells
• The epithelial component can form glands, cords, or nests and the tumor cells are characterized by ovoid nuclei and abundant cytoplasm. Limited biopsies may only sample the glandular component, leading to an erroneous diagnosis of adenocarcinoma
• The spindle cell component is arranged in dense cellular sheets or vague fascicles; most display prominent hemangiopericytoma-like vessels. A variable amount of stromal and focal myxoid change is often observed. Microcyst formation is not uncommon and mast cells may be abundant. The spindled tumor cells have uniform, oval to round nuclei, sparse cytoplasm, and indistinct cell borders, which creates the appearance of overlapping nuclei
• Similar to primary pulmonary SS, primary cardiac SS is predominantly seen as the monophasic spindle cell subtype, lacking glandular structures
• The monophasic glandular subtype is remarkably rare
Immunopathology/special stains
• The current gold standard for diagnosis of SS is the demonstration of t(X;18), or SYT-SSX fusion product, by fluorescence in situ hybridization (FISH), reverse transcriptase-polymerase chain reaction (RT-PCR), or cytogenetics combined with morphology. However, IHC can be useful in narrowing the differential diagnosis
• In SS, the most useful positive markers are cytokeratins, epithelial membrane antigen (EMA), CD99, BCL2, and transducin-like enhancer-1 (TLE1), whereas some key negative markers are used to rule out other entities
• t(X;18)(p11;q11) is specific for SS and can be detected cytogenetically in more than 90% of cases
Main differential diagnoses
• Metastatic SS: clinical history
• Spindle cell carcinoma: negative for BCL2, CD99,TLE1, and t(X;18)
• Malignant mesothelioma: also biphasic but exhibits a unique immunohistochemical profile; does not arise from the atria
• Solitary fibrous tumor: usually lower grade; strongly expresses CD34
• Ewing sarcoma: a distinct genetic and immunohistochemical profile
Fig 1 Synovial sarcoma of the heart. A, In this biphasic tumor the epithelial component is poorly defined. B, The spindle cell component has scant cytoplasm, oval nuclei, and some prominent nucleoli. Note mitotic figure and characteristic cellular overlap.
Fig 2 Synovial sarcoma of the heart. Nuclear staining for TLE1.