145P The first epidemiological and histopathological study of soft tissue sarcoma in Latvia

Background: Extraosseous Ewing's sarcoma (EES) is a rare, aggressive malignancy constituting 20%-30% of all Ewing's sarcomas (ES).Comprehensive studies on EES from low-and middle-income countries (LMICs) are rare.We analyzed a 12-year cohort of EES from a tertiary care cancer center to gain deeper insights.Methods: Between January 2010 and December 2022, all newly diagnosed and managed EES cases were retrieved for analysis.Results: EES constituted 34.2% (n145) of all ES cases (n424).The median age was 20 years, and 51.7% were female.The majority had localized disease (75.1%, n109).The most common tumor locations were the chest wall (35.1%) and thigh (14.5%).ES of viscera was seen in 15.9% (n 23), predominantly in the genitourinary tract (65%).Pain (89.6%) and swelling (75.2%) were the most common symptoms.Due to financial constraints, fluorescent in situ hybridization (FISH) was performed in only 5.5% of cases.Treatments included neoadjuvant chemotherapy (83.5%, n91), surgery (40.4%, n44), radiotherapy (52.3%, n57), and adjuvant chemotherapy (94.5%, n103).Only 67% (n73) of localised disease completed the planned treatment.Tumor necrosis >90% was observed in 62.5% of post-chemotherapy surgical specimens.The median follow-up was 62 months, with 83 patients (57.2%) alive.The 5year and 10-year overall survival (OS) rates for all cases were 60% and 52%, respectively, while the 5-year and 10-year event-free survival (EFS) rates were 55% and 51%, respectively.Univariate analysis identified metastatic disease, elevated lactate dehydrogenase levels, incomplete treatment, and margin positivity as factors associated with poorer outcomes.However, on multivariate analysis, treatment completion was the sole prognostic factor influencing survival.Notably, the median OS and EFS were not reached.Conclusions: Our study on EES represents the largest dataset from LMICs.Affordability and access to novel diagnostics and therapeutics pose great challenges.Early diagnosis, treatment, compliance, and follow-up are severely affected by socio-economic factors.The EFS and OS noted in our study highlight these dynamics and underscore areas for improvement.