(P 370) SYNOVIAL SARCOMA; ROLE OF ADJUVANT CHEMOTHERAPY IN SURGICALLY TREATED PATIETNS WITH NO METASTASIS; A SEER STAT ANALYSIS.

Objective: Synovial sarcoma is known to be a unique subset of soft tissue sarcomas. Most types of sarcomas are chemo-resistant. However, regarding synovial sarcoma, there has been a debate whether it is considered chemo-sensitive or not. So, we aim to assess survival outcomes of adjuvant chemotherapy in surgically treated patients with non-metastatic synovial sarcoma.

Methods: In this retrospective cohort study, we extracted the data of 815 patients from the Surveillance, Epidemiology, and End Results (SEER) database whom were diagnosed between 2000-2019. All of them had Synovial Sarcoma with M0 disease. Stages I, II and III are considered in nodal negative patients. The diagnosis of stage IV synovial sarcoma is either based on N1 disease or M1 disease, so in this study we only included Surgically treated N1 Stage IV synovial sarcoma. The classification of tumor staging, nodal staging and metastasis were according to eighth edition of AJCC. We calculated the 5-year relative survival for patients who had adjuvant chemotherapy versus patients with no systemic therapy. Kaplan-Meier curve and log rank test were performed using SPSS 25 for survival analysis.

Results: The overall 5-year survival was 78.6%; P< 0.001. The 5-year relative survival of adjuvant chemotherapy(n=383) versus no systemic therapy(n=432) were 72% and 84.9% respectively; P< 0.001. With stratification by staging, the overall 5-year survival of adjuvant chemotherapy versus no systemic therapy were Stage I (76.2%, 90.4%; P< 0.001), Stage II (69.3%, 87.3%; P< 0.001), Stage III (63.4%, 67.5%; P< 0.001) and Stage IV (71.9%, 25.7%; P< 0.001. The median overall survival (OS) was 126 months in adjuvant arm and 152 months in patients with no systemic therapy.

Conclusion: Synovial Sarcoma has an overall favorable outcome. Adjuvant chemotherapy proved an overall no survival benefit compared to no systemic therapy. With stratification staging, Nodal negative Stages I, II and III patients showed better outcomes with no adjuvant chemotherapy. However, stage IV with Nodal metastasis benefited from adjuvant chemotherapy by 3 folds compared to no systemic therapy. In conclusion, stage IV synovial sarcoma are usually not indicated for surgery but if surgery was recommended for a selected patient, we recommend adjuvant chemotherapy only in nodal positive stage IV synovial sarcoma.