Uterine sarcomas make up 1-4% of uterine malignancies. Of these 60% are classified as leiomyosarcoma (uLMS). The 5-year survival rate of uLMS is 35-65.2% for tumours that have not spread beyond the uterus. However, women are often diagnosed at a late stage due to a lack of screening options by which time the tumour has often spread to adjacent and distant tissues. Current standard of care for uLMS patients is surgical de-bulking followed by adjuvant chemotherapy, but significant improvement in progression free survival and overall survival is not consistently observed. The lack of advances for the treatment and screening of uLMS is due in part to the scarcity of appropriate research resources for this rare disease. Genetic analyses have been performed but on relatively small samples and there are just 14 reported patient-derived xenograft (PDX) models of uLMS in the literature to date. Through the WEHI Stafford Fox Rare Cancer Program, as well as collaborations (facilitated by ANZGOG) throughout the country and internationally, we have access to a large biobank of uLMS tissue. We have received 8 fresh uLMS samples in the laboratory, 2 of which have established PDX lines that were validated as uLMS by our anatomical pathologist. All fresh samples received into the laboratory are snap frozen for whole-genome sequencing as well as viably frozen to enable regeneration of the tissue for future applications. One application is organoid culturing, which allows the tissue to retain its 3D growth properties and is significantly cheaper than growing tissue as a PDX. Organoid culturing also allows for higher throughput of samples in drug screening assays, enabling us to fast-track the selection of drugs for validation in our PDX models. In addition to these fresh samples we also have 23 archival uLMS samples (formalin fixed, paraffin embedded) that can be used for lower coverage genetic analysis, and protein expression by immunohistochemistry. This unique biobank of uLMS tissue is the first of its kind in Australia and with it we will endeavour to gain a comprehensive understanding of this disease. Through our PDX modelling we also have the opportunity to predict resistance to therapy and test emerging therapies in a clinically relevant context. We believe this biobank will provide a critical resource which will ultimately lead to better outcomes for uLMS patients. Citation Format: Genevieve Dall, Cassandra Vandenberg, Amandine Carmagnac, Ratana Lim, Briony Milesi, Angela Komiti, Emily O'Grady, Joshua Tram, Gayanie Ratnayake, Kym Pham Stewart, Justin Bedo, Jocelyn Penington, Joep Vissers, Inger Olesen, Sean Grimmond, Holly Barker, Tony Papenfuss, Clare Scott. Developing pre-clinical models of uterine leiomyosarcoma [abstract]. In: Proceedings of the AACR Virtual Special Conference: Endometrial Cancer: New Biology Driving Research and Treatment; 2020 Nov 9-10. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(3_Suppl):Abstract nr PO021.