e23551 Background: Current therapeutic options for advanced synovial sarcomas remain limited. Adoptive T-cell therapies against NY-ESO-1 and MAGE-4 benefit a subset of patients, but is of limited value in Asian patients due to the absence of the HLA-A*02 genotype. Methods: The trial had a single arm, Simon two-stage design that included patients with advanced synovial sarcomas who had progressed on 2 lines of therapy, one of which could be an anti-VEGF therapy. Regorafenib was administered orally in a continuous regimen with 80mg and 120 mg doses on alternate days. The primary end point was 3-month progression-free rate (PFR). A 3-month PFR of greater than 40% was taken to be a marker of drug efficacy. Secondary end points included median PFS, OS and safety analysis. Quality of life assessment was carried out at baseline and at 3 months using the EORTC C-30 questionnaire. Radiological responses were assessed using RECIST 1.1 criteria after independent review by 2 radiologists. Results: A total of 22 patients were included in the study during the period from January 2022 to December 2023 with baseline characteristics as shown in Table 1. 18 patients were eligible for assessment of the primary outcome. The 3-month PFR with regorafenib was 57% with an ORR of 5%. At a median follow up of 9 months, the median PFS was 5.0 (2.9-7.0) months, and the median OS was 10.0 (7.8-11.2) months. In an exploratory analysis, the subset of patients previously exposed to pazopanib showed a 3-month PFR of 46% and a median PFS of 3 months. The grade ¾ toxicities seen included HFSR (52%), diarrhea (5%) and oral mucositis (5%). The quality-of-life analysis showed symptom burden to be highest in the fatigue, pain and financial difficulties domain at baseline. No worsening of symptom burden scores was seen over the study period. The global health status score showed a numerical improvement at 3 months. Conclusions: The study had a significant number of patients with poor PS. Regorafenib in the above-mentioned dosing regimen demonstrated meaningful clinical activity in a heavily pre-treated population of patients with synovial sarcoma, including those previously exposed to pazopanib, with a preserved quality of life. The treatment was associated with manageable toxicities and no new safety signals, albeit with higher HFSR rates. [Table: see text]