Primary mediastinal synovial sarcoma in an infant: A case report

Abstract Background Primary mediastinal synovial sarcoma (PMSS) is an uncommon and aggressive soft tissue tumor, particularly rare in infants. Its diagnosis is challenging due to overlapping features with other thoracic neoplasms and requires integration of histopathology, immunohistochemistry, and molecular genetics. Case presentation We present a case of a 4‐month‐old girl admitted with respiratory distress and found to have a large posterior mediastinal mass. Histopathology and immunohistochemistry were compatible with biphasic synovial sarcoma. However, molecular confirmation via detection of SS18‐SSX fusion was not performed. Despite multimodal chemotherapy, the tumor progressed, and complete surgical resection was unachievable. The patient died during follow‐up in the pediatric intensive care unit. Conclusion Accurate diagnosis is critically dependent on SS18‐SSX molecular testing, particularly in infants. Incomplete resection and lack of genetic confirmation may contribute to poor prognosis. Literature supports that complete resection is the only consistent predictor of survival. This case illustrates the limitations and consequences of managing PMSS without molecular confirmation or complete resection. A multidisciplinary approach with current diagnostic standards is essential in these high‐risk pediatric tumors.