S3332 Pancreatic Mass as a Rare Recurrence of Synovial Sarcoma: A Case Report

Introduction: Synovial sarcoma (SS) is a rare, aggressive soft tissue malignancy typically arising in the lower extremities of young adults. Over 50% of patients have recurrence within 2 years, most commonly to the lungs, lymph nodes, or bone. Pancreatic metastasis is extremely rare, with only a few reported cases. We present a case of biphasic SS arising in the right thigh, which recurred as a solitary pancreatic metastasis in a 55-year-old man after an extended disease-free interval. Case Description/Methods: A 55 year-old man with a history of stage IIIB biphasic synovial carcinoma of the right thigh underwent neoadjuvant radiation and surgical resection without adjuvant chemotherapy. Surveillance imaging included computed tomography chest every 3 months and magnetic resonance imaging femur every 6 months, with stable subcentimeter pulmonary nodules and no evidence of recurrence or metastasis. He underwent computed tomography scan of the chest for surveillance imaging after a 4 year disease-free interval, which revealed a large pancreas head mass. Abdominal computed tomography revealed a mass in the pancreatic head and uncinate process, possibly involving the portal and mesenteric veins. Subsequent endoscopic ultrasound showed 2 irregular, hypoechoic pancreatic masses in the head and a hypoechoic well rounded mass in the tail. Fine needle biopsy confirmed malignant cells consistent with SS in the pancreatic head and tail. Fluorescence in situ hybridization analysis demonstrated SS18 (SYT) rearrangement, confirming metastatic SS. Discussion: In this case report, the patient’s asymptomatic presentation and absence of prior metastatic disease to common sites such as the lungs lowered clinical suspicion. Standard surveillance for extremity soft tissue sarcomas (eSTS) focusemetastasectomyite and chest imaging. This case highlights the potential value of incorporating abdominal imaging into long-term follow-up, even in asymptomatic patients, given the possibility of rare metastatic spread. Prognosis varies based on metastatic burden, resection completeness, and systemic therapy response. Solitary lesions may have better outcomes, as seen in a case report with 3 years of recurrence-free survival. In contrast, another case report described rapid progression and death within 2 months with lung metastases. In addition, poorly differentiated SS (PDSS) carries a higher risk of recurrence and worse outcomes; 1 patient with PDSS died 3 months after extrapleural pneumonectomy. These findings underscore the need for more research on pancreatic SS metastasectomy, particularly in high-risk subtypes.