e23327 Background: Retroperitoneal leiomyosarcoma (RPL) is an exceedingly rare malignancy and is the second most common subtype of leiomyosarcomas. Most of the information concerning this rare disease is limited to case studies and few literature studies. The study's objectives were to assess the demographics, pathological factors, survival outcomes, genomic landscape and potential for targeted therapy. Methods: Data of retroperitoneal leiomyosarcoma were obtained from the Surveillance, Epidemiology, and End Results (SEER) database, with cases diagnosed between 2000 and 2020 used for this study and the Cancer Genome Atlas containing sequencing information for 27 cases of RPL. Results: A total of 1406 cases were extracted with mean age of diagnosis of 62.1 years. Of these, RPL had a higher incidence in women (71.5%), more cases affected Whites (58.7%). Histologically, in patients with known grading, most patients’ i.e. 62.35% were grade 3, G3 (poorly differentiated). Nearly all (99.9%) patients presented with a tumor size ≥4.1 cm. Local lymph nodes metastasis were positive in 76.0% of cases when lymph node status was reported. In known cases of distant metastases, the most common site was liver (8.9%). The main treatment modality was surgery only (26.7%, hazard ratio, HR 1.17, p-value < 0.001), followed by the standard of care (surgery and radiation) (18.4%, HR 1.03, p-value < 0.001), and radiation only (18.4%). Five-year overall survival was 40% and 5-year cause-specific survival was 64%. The highest 5-year survival was observed in patients undergoing surgery and radiation (57%), and in combination therapy (chemotherapy, surgery, and radiation) the 5-year survival was 39%. Genetic analysis found the most common mutations included TP53 (51.9%), RB1 (25.9%), and ATRX (14.8%). When accounting for deep deletions and rearrangements, total frequency of the alterations was higher such that TP53 (63.0%), RB1 (51.9%), and ATRX (18.5%). Potentially actionable alterations were rare but included activating alterations in FGFR1, PIK3CA and ESR1, as well as deep deletions of BRCA1. Conclusions: Retroperitoneal leiomyosarcoma is a very rare tumor where surgery and radiation has been the conventional therapy. Our study indicates there are genetic alterations in the majority of retroperitoneal leiomyosarcoma. To further understand the pathogenesis and survival factors, patients with RPL should be enrolled into national and international registries.