Primary Synovial Sarcoma of the Abdomen and Pelvis

Synovial sarcoma (SS) of the abdomen and pelvis is a rare and understudied condition. This study aimed to evaluate survival outcomes, assess calculated versus observed outcomes, and describe radiographic features among patients with localized abdominal/pelvic SS.

A retrospective chart review of 58 patients diagnosed with localized abdominal/pelvic SS between 1992 and 2022 was performed. Overall survival (OS), local recurrence-free survival (LRFS), and metastasis-free survival (MFS) were assessed. Sarculator-predicted 5-year OS and disease-free survival (DFS) were compared with observed outcomes.

Twenty-four (41%) patients had tumors located in the extra-abdominal/pelvic region, and 34 (59%) had tumors located in the intra-abdominal/pelvic region. Most of the patients were female (62%). Survival outcomes revealed a median OS: 5.5 years, 5-year OS: 53%, median MFS: 1.5 years, and 5-year MFS: 32%. Patients with intra-abdominal/pelvic tumors had significantly worse MFS than those with extra-abdominal/pelvic tumors (median 1.3 vs. 2.7 y; P =0.023). Larger tumor size (≥5 cm MFS HR: 4.20, 95% CI: 1.48-11.95), poorly differentiated histology (MFS HR: 2.92, 95% CI: 1.13-7.53), and positive/unknown margins (OS HR: 2.96, 95% CI: 1.29-6.78; LRFS HR: 6.61, 95% CI: 1.65-26.50; MFS HR: 2.45, 95% CI: 1.23-4.89) were associated with worse outcomes. Sarculator-predicted and observed 5-year OS (49% vs. 52%) and DFS (30% vs. 26%) were consistent. Imaging features such as cystic changes and calcification were more frequent in larger and monophasic tumors.

In localized abdomen/pelvic SS patients, tumor size, location, and surgical margins are critical prognostic factors. Sarculator may aid in risk stratification.