Abstract Background Synovial sarcoma is a rare and aggressive soft tissue malignancy that most often arises in the extremities of young adults. Primary mediastinal synovial sarcoma (MSS) is exceptionally uncommon, representing fewer than 1% of mediastinal tumors. Because of its overlapping histologic features with lymphoma and other small round blue cell tumors, it is prone to diagnostic confusion, often leading to delayed or inappropriate treatment. Case Presentation We describe a 45-year-old Filipina who was incidentally found to have an anterior mediastinal mass on chest imaging. A needle biopsy performed at an outside facility was initially read as a small round blue cell tumor, and she was treated as a case of non-Hodgkin lymphoma with CHOP followed by ABVD plus rituximab. After six cycles, she showed only partial response on imaging. Upon referral to the Philippine General Hospital, slide review revealed a spindle-cell proliferation inconsistent with lymphoma. Repeat biopsy and immunohistochemistry favored a diagnosis of synovial sarcoma, with SS18 gene rearrangement testing recommended for confirmation. A multidisciplinary tumor board involving Thoracic Surgery, Medical Oncology, Pulmonology, Pathology, and Radiology deemed the mass resectable. The patient underwent successful complete resection, with final histopathology confirming spindle-cell synovial sarcoma. She is currently being prepared for adjuvant ifosfamide-doxorubicin chemotherapy and interval CT-based surveillance. Discussion This case illustrates the diagnostic pitfalls of MSS, particularly in resource-limited settings where immunohistochemistry and molecular testing are not always accessible. Multidisciplinary review and centralized pathology reassessment were instrumental in arriving at the correct diagnosis and in formulating an appropriate treatment plan. Conclusion Primary mediastinal synovial sarcoma is an exceptionally rare entity that can mimic more common mediastinal neoplasms. Accurate diagnosis requires a high index of suspicion, appropriate use of immunohistochemical and molecular tools, and coordinated multidisciplinary care. This case is noteworthy for its initial misclassification and eventual successful management through collaborative, guideline-based decision-making in a Philippine tertiary center. This abstract is funded by: myself
Cledera et al. (Fri,) studied this question.
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