124P Ewing's sarcoma in adolescents and adults: 12-year experience from a reference center in Peru

Ewing's Sarcoma (ES) belongs to a group of rare and aggressive tumors, 30% have metastases at the onset; the average age of patients is between 10 and 20 years. This study aimed to assess the clinical-pathological characteristics, presentation, and treatment modalities for local control, as well as associated adverse events. An observational, descriptive, cross-sectional, and retrospective study was conducted, including patients over 14 years old diagnosed with Ewing's Sarcoma between 2010 and 2022 at the Instituto Nacional de Enfermedades Neoplásicas Lima-Peru. The study involved 40 patients aged over 14, with a median age at diagnosis of 20 years (62.5% male, 37.5% female). The average time from symptom onset to diagnosis was 6 months. Predominant symptoms were tumor formation (89%) and pain (52.5%). 40% had tumors over 8 cm, with 25% localized, 30% locally advanced, and 45% metastatic. Common locations were lower limb (60%), upper limb (12.5%), spine (10%), and 7.5% extra-skeletal. Diagnostic studies showed elevated LDH (80%) and anemia (20%). Immunohistochemical analysis indicated positivity for CD99 (89.2%) and FLI1 (92.6%). 57.5% received neoadjuvant treatment, 21.7% had surgery post-chemotherapy (VAC/IE, 87%), and 26% experienced grade 4 toxicity. 17.5% underwent initial surgery, all receiving adjuvant chemotherapy (VAC/IE). At analysis, 51.5% experienced disease progression, and 30% died. This is the first study describing the ES in Adolescents and Adults in Peru. 75% of patients are diagnosed with advanced disease, which translates into a higher recurrence and mortality rate. The VAC/IE regimen is the most used, a future analysis is required to evaluate the result in terms of survival and toxicity. We need to develop strategies that allow us to improve the diagnosis rate in earlier stages in the reference center.