(P 02) PEDIATRIC SYNOVIAL SARCOMA: A REVIEW OF 21 CASES FROM A SINGLE INSTITUTION

Objective: Synovial sarcoma is rare, yet remains the most commonly diagnosed soft tissue sarcoma in childhood and adolescent patients. There are few studies reporting on the outcomes of synovial sarcoma in patients under 18 years of age. We sought to describe the rates of recurrence and disease-specific survival in pediatric patients diagnosed with synovial sarcoma.

Methods: We retrospectively reviewed the medical records of 361 patients with synovial sarcoma. Twenty-one patients (6%) were diagnosed with synovial sarcoma prior to the age of 18. All patients were evaluated at a single institution between 2000 and 2020. Mean age at diagnosis was 11 years (range 4 – 17) and 13 patients (62%) were male. Nineteen primary lesions were located in the extremity, one tumor was located in submandibular region, and one tumor was located in the buttock. The mean maximum pre-treatment dimension of primary lesions was 4.7±2.8cm (range 1.1-10.8). Seven patients were diagnosed via contaminated excisional biopsy. Fifty-two percent of tumors were of the monophasic subtype and the remainder were biphasic. Median follow-up for survivng patients was 62 months (range 9-192).

Results: All patients underwent surgical treatment of the primary lesion in the form of limb salvage. Seven patients with low risk lesions ( < 5cm, completely resected) were treated with surgery alone. Eleven patients received both perioperative chemotherapy (doxorubicin/ifosfamide [n=9], VDC/IE [n=2]) and radiotherapy. Three patients received perioperative radiotherapy (mean 50Gy) without chemotherapy. Two patients had positive margins, one of which was a planned intralesional procedure and was managed via brachytherapy and the other was an unplanned positive margin that was addressed with post-operative radiation.
Eleven patients (52%) underwent reoperation for infection/wound complications (n=5), scar tissue (n=2), recurrence (n=2), leg length discrepancy following rotationplasty (n=1), and amputation for radiation-associated osteosarcoma (n=1). Three patients developed local recurrence at 5, 20, and 21 months. Only one of these patients had positive margins. Four patients developed lung metastases at a mean 20 months from biopsy. All four patients who developed metastases ultimately succumbed to disease. Mean survival from metastatic diagnosis was 11 months (range 4-21). Recurrence-free survival (RFS) at 1 and 5 years was 95% and 73%, respectively. Disease-specific survival (DSS) was 100% at 1 year and 78% at 5 years. Compared with adult patients with synovial sarcoma, pediatric patients had a lower risk of recurrence (HR 0.36, 95% CI [0.15, 0.90], p=0.02) and higher disease-specific survival (HR 0.38, 95% CI [0.14, 1.05], p=0.05) (Figures 1 &2)

Conclusion: Pediatric patients comprise a small percentage of patients diagnosed with synovial sarcoma. Local control including limb salvage surgery and perioperative radiotherapy resulted in low rates of local recurrence, but high rates of reoperation. Compared with adult patients, pediatric patients have higher recurrence-free and disease-specific survival rates. Overall, surgical treatment of pediatric synovial sarcoma with neoadjuvant or adjuvant chemoradiation, when indicated, results in high 5-year survival for the majority of patients.