(P 465) UNPLANNED EXCISION OF SYNOVIAL SARCOMA: FACTORS ASSOCIATED WITH RECURRENCE AND SURVIVAL

Objective: Synovial sarcoma is rare and may present as a small, slow-growing mass. These tumors are often mistaken as benign and are therefore prone to unplanned and/or non-oncologic excision. We sought to identify the rate of unplanned excision of synovial sarcoma and risk factors for recurrence and survival among this cohort.

Methods: The medical records of 160 patients evaluated at a single institution for synovial sarcoma between 1997 and 2021 were retrospectively reviewed. Of these, fifty-three (33%) who underwent unplanned, non-oncologic excision of synovial sarcoma were included. Mean age of the cohort was 37±16 years. Primary lesions were located in the extremity (n=36), abdomen (n=4), thorax (n=7), or head/neck (n=6). The medium maximum pre-treatment dimension of the primary lesion was 3.6cm (range 0.9-14). Fifty (94%) patients underwent re-excision of the tumor bed, 25 received chemotherapy and 39 received radiation therapy. Univariate and multivariate analysis were performed to analyze the effect of risk factors on recurrence-free survival (RFS) and disease-specific survival (DSS).

Results: Twenty-three patients (46%) had no residual tumor on re-excision, all but two of which had received pre-operative radiotherapy. Four patients (two abdominal, one mediastinal, and one popliteal fossa tumors) had positive margins after re-resection. Three of these (two abdominal, one mediastinal tumors) patients developed local recurrence followed by metastatic disease and subsequent death. Four additional patients (9%) developed local recurrence despite margin-negative resection, and three of these patients developed metastases followed by death. Of patients who did not develop local recurrence following margin-negative re-resection, 14% (n=6 of 44) developed metastases; all of these patients subsequently died of their metastatic disease. All three patients who did not undergo re-excision developed recurrence or succumbed to their disease. In the overall cohort, RFS at 1 and 5 years was 85% and 70%, respectively (Figure 1). DFS at 1 and 5 years was 96% and 75%, respectively (Figure 2).
On univariate analysis, positive prognostic indicators for recurrence and survival included extremity location, absence of bone involvement, size < 5cm, perioperative radiation, and absence of residual tumor on re-excision (p < 0.05). When controlling for tumor size and presence of residual tumor, the use pre-operative radiotherapy was associated with lower RFS (HR 0.18, 95% CI [0.04, 0.77], p=0.02) and DSS (HR 0.17, 95% CI [0.04, 0.81], p=0.03) on multivariate analysis. Chemotherapy was not associated with improved outcomes on univariate or multivariate analysis (p>0.1)

Conclusion: One-third of patients presenting with synovial sarcoma were diagnosed after unplanned, non-oncologic excision. Patients with large, truncal tumors had worse survival. Approximately half of patients who underwent unplanned excision had no residual tumor after pre-operative radiation. The use of radiation was associated with improved rates of recurrence and disease-specific death. Our results suggest that margin-negative re-resection and pre-operative radiotherapy should be considered when feasible following unplanned excision of synovial sarcoma.