Primary Cardiac Synovial Sarcoma (PCSS): Clinicopathologic Features of 6 Cases and Literature Comparison.

Primary cardiac synovial sarcoma (PCSS) is an exceedingly rare tumor. This study presents a comprehensive analysis of six novel PCSS cases identified within our institutional cohort, compared with published literature cohorts, focusing on their clinical presentations, histopathological features, immunohistochemical and molecular characteristics, therapeutic interventions, and prognosis. Our institutional cohort included five male and one female patients, with a median age of 44 years. Presenting symptoms included dyspnea, chest tightness, back pain, and syncope. Tumors were located in the pericardium (four cases) and the cardiac wall (two cases). The tumor size ranged from 2.0 to 14.5 cm. Histopathologically, four cases were monophasic and two were biphasic. Immunohistochemical analysis revealed consistent expression of TLE1, vimentin, and BCL-2. Molecular analysis confirmed the presence of the SS18-SSX gene fusion through fluorescence in situ hybridization (FISH) in five cases, whereas one FISH-negative case was positive for the SS18-SSX1 gene fusion through next-generation sequencing (NGS). All patients underwent surgical intervention (tumor excision) followed by adjuvant chemotherapy with doxorubicin and ifosfamide. At follow-up, four patients were alive without disease and two had died. This case series highlights the clinicopathologic and molecular features of PCSS. Overall, SS18 (SYT) gene rearrangement and TLE1 expression are crucial diagnostic markers for differentiating PCSS from other neoplasms.