11564 Background: Soft tissue sarcomas (STSs) are a heterogeneous group of cancers with high unmet need. Trabectedin (T) is an FDA-approved chemotherapy that blocks cell cycling and DNA repair pathways. Combination T and conventional radiation (XRT) in STS nonrandomized phase 1/2 trials demonstrated objective response rates (ORR) of 36-72% in localized and low burden metastatic disease, while pre-treated metastatic STS treated with T alone has an ORR of 10-14%. We hypothesize that the combination of T and hypofractionated radiation (hXRT) will exhibit a tolerable safety profile and improve ORR relative to historical outcomes with T or hXRT alone. Here we report our experience in the treatment of oligometastatic STS with combined T and hXRT. Methods: We reviewed our institutional experience to identify patients treated with T and XRT. We included patients with high risk localized or metastatic STS (majority of patients had metastatic disease at time of treatment). All patients received at least 1 cycle of T and concurrent XRT to at least 1 lesion. ORR and local control rate (LCR) were determined for irradiated lesions by RECIST 1.1. Results: Between 2020 – 2021, 9 STS patients with 21 tumors were treated at the University of Colorado with XRT and concurrent T. The median age was 39.2 (range 26.0 – 64.6) years. 8 patients had metastatic disease at the time of treatment. Treated tumor sites included 1 lung,1 extremity, 2 liver, 2 retroperitoneal, 5 bone, and 10 peritoneal. The following histologic subtypes were included: myxoid liposarcoma (3), uterine leiomyosarcoma (2), non-uterine leiomyosarcoma (1), dedifferentiated liposarcoma (1), undifferentiated pleomorphic sarcoma (1), and synovial sarcoma (1). All metastatic patients were pre-treated with a median of 3 lines of systemic therapy. The median number of T cycles delivered was 5 (range 1 – 20). The median XRT prescription dose was 3000cGy (range 2000cGy – 5000cGy), with 8 patients having received hXRT (5 -10 fractions) and 1 having received conventionally fractionated XRT. 8 patients underwent 1 course of XRT, while 1 received 3 courses in combination with T. All patients had a Karnofsky performance status equal to or greater than 60. After a median follow-up 5.4 months, the LCR of treated lesions was 90.5%. The ORR (CR or PR) was 57.1% and median decrease in tumor diameter at time of maximum response was 52.0%. The median time until maximum response was 3.7 months. 2 patients experienced grade 3 toxicity (LFT elevation) attributable to T, and 2 patients experienced grade 3 toxicity due to XRT. There were no grade 4 or 5 toxicities. Conclusions: T in combination with hXRT appears to be safe and feasible in this patient population. Based on these data, a phase 1/2 prospective clinical trial is being planned in oligometastatic and high risk localized STS. Table: see text