Riverside University Health System Moreno Valley, CA
Mena Saad, DO1, Medora Doris. Rodrigues, MD, MPH2, Raymond Huang, MD1, Matthew Orosa, DO1, Ronaldo Gnass, MD1, David Liu, MD1, Han Koh, MD1, Steve Serrao, MD1, Alexander W.. Jahng, MD3 1Riverside University Health System, Moreno Valley, CA; 2The Ohio State University Wexner Medical Center, Columbus, OH; 3Loma Linda University Medical Center, Loma Linda, CA Introduction: Synovial sarcoma is a rare and aggressive soft tissue malignancy. Its pathogenesis is defined by a specific chromosomal translocation, t(X;18)(p11;q11), resulting in the SS18-SSX fusion protein, which drives tumor progression. This sarcoma typically arises in deep soft tissues near large joints, especially in the extremities, and most commonly affects adolescents and young adults (ages 15–40). Metastasis to the pancreas is exceptionally uncommon, with only a handful of cases reported in the literature.
Case Description/
Methods: A 40-year-old male with a history of synovial sarcoma of the left lower extremity—initially misdiagnosed as Ewing sarcoma 8 years prior and later reclassified—status post left lower extremity amputation and chemotherapy, presented with cough, hemoptysis, and unintentional weight loss. He had recently undergone rigid bronchoscopy with ablation of a vascular endobronchial tumor suspected to be metastatic sarcoma. Vital signs were stable, and laboratory studies were largely unremarkable. Computed tomography (CT) of the chest revealed a new left lower lobe consolidation. He underwent left thoracotomy with lower lobectomy and intercostal nerve cryoablation. Histology demonstrated small round blue cells, with immunohistochemistry (IHC) staining positive for SS18-SSX/SSX C-term, confirming poorly differentiated metastatic synovial sarcoma. A surveillance CT scan one year later showed no evidence of recurrence. However, six months after that, a follow-up CT abdomen and pelvis revealed a new 6 cm non-enhancing lesion in the pancreatic tail. Magnetic resonance imaging (MRI) of the abdomen and pelvis further characterized the lesion as a solid mass measuring 4.7 x 5.3 x 4.6 cm. CT-guided biopsy confirmed metastatic synovial sarcoma to the pancreas. Positron emission tomography (PET) scan revealed no evidence of additional metastatic disease beyond the pancreatic mass. Discussion: Synovial sarcoma is an aggressive malignancy that can mimic other high-grade sarcomas histologically. Immunohistochemistry for the SS18-SSX fusion protein remains the most sensitive and specific marker for diagnosis. Most common sites of metastasis for synovial sarcoma are the lungs, followed by lymph nodes and bone. Pancreatic metastasis is exceedingly rare and makes overall management difficult. Surgical resection is the mainstay of treatment with isolated metastasis to the pancreas.
Figure: Figure 1A. CT demonstrates left lower lobe mass (red arrow). Figure 1B. Follow up CT after left lower lobectomy. Figure 1C. Surveillance CT 1 year later demonstrating hypo-enhancing pancreatic tail mass (yellow arrow). Figure 1D. MRI demonstrates pancreatic tail mass with heterogeneous enhancement (blue arrow). Figure 1E & Figure 1F. FDG PET/CT 3 months after MRI shows interval size increase of pancreatic tail mass with metabolic activity similar to background pancreatic parenchyma and areas of photopenia (blue arrow) which correlates to the necrotic areas (red arrow).
Figure: Figure 2. Fragment of tumor showing malignant spindle/round neoplastic cells. H&E 100x.
Disclosures: Mena Saad indicated no relevant financial relationships. Medora Rodrigues indicated no relevant financial relationships. Raymond Huang indicated no relevant financial relationships. Matthew Orosa indicated no relevant financial relationships. Ronaldo Gnass indicated no relevant financial relationships. David Liu indicated no relevant financial relationships. Han Koh indicated no relevant financial relationships. Steve Serrao indicated no relevant financial relationships. Alexander Jahng indicated no relevant financial relationships.
Mena Saad, DO1, Medora Doris. Rodrigues, MD, MPH2, Raymond Huang, MD1, Matthew Orosa, DO1, Ronaldo Gnass, MD1, David Liu, MD1, Han Koh, MD1, Steve Serrao, MD1, Alexander W.. Jahng, MD3. P2308 - A Rare Case of Pancreatic Metastatic Synovial Sarcoma, ACG 2025 Annual Scientific Meeting Abstracts. Phoenix, AZ: American College of Gastroenterology.
