ESTRO 2025 - Abstract Book

S1689

Clinical - Sarcoma & skin cancer & malignant melanoma

ESTRO 2025

chemotherapy. RT was administered postoperative and definitive in 20 and 17 (45.9%) patients, respectively. 28 patients (75.7%) received local PT only with a median dose of 54.0Gy (range 45.0-59.4Gy). Hemithorax RT was administered in nine patients to a median dose of 18.0Gy (range 12.0-18.0Gy). During the median follow up time (from first diagnosis until last contact) of 2.7 years (range 0.5-8.9 years), eight patients experienced metastatic recurrence (n=5 lung, n=2 bone, n=1 liver, n=1 soft tissue) and five patients local progression. Seven patients died of systemic failure (n=4) or local failure (n=3). 27 patients experienced acute >°2 toxicities (n=27 blood, n=3 skin). Seven patients developed >°2 late toxicities (n=2 blood, n=2 weight gain, n=2 nervous system, n=1 GI, n=1 fracture). Conclusion: PT for patients with thEwS was well tolerated with reasonable toxicities and promising local tumor control in the majority of patients. So far, no acute or late cardiopulmonal toxicities were observed. Still, larger cohorts with long term function monitoring are sought to confirm these findings.

Keywords: thoracal ewing sarcoma, proton therapy, outcome

2549

Digital Poster Long-term outcomes of myxofibrosarcoma: A 24-year retrospective analysis from a single Institution Ricardo Clairefont Dias Regis 1 , Fernando Augusto Batista Campos 2 , Suely Akiko Nakagawa 3 , Samuel Aguiar Junior 4 , Antônio Cássio Assis Pellizzon 1 , Gabriela Dall Agnol 5 , Maria Letícia Gobo Silva 1 1 Department of Radiation Oncology, AC Camargo Cancer Center, São Paulo, Brazil. 2 Department of Clinical Oncology, AC Camargo Cancer Center, São Paulo, Brazil. 3 Division of surgery, department of orthopedics, AC Camargo Cancer Center, São Paulo, Brazil. 4 Division of surgery, department of sarcoma, AC Camargo Cancer Center, São Paulo, Brazil. 5 Department of statistics, AC Camargo Cancer Center, São Paulo, Brazil Purpose/Objective: Myxofibrosarcoma (MFS) is a rare and aggressive soft tissue tumor, accounting for approximately 5% of all soft tissue sarcomas (STS). It is characterized by a high local recurrence (LR) rate compared to other STS, with reported rates ranging from 17% to 54% 1 . This institutional study aims to analyze the recurrence rate of MFS following surgery and radiotherapy (RT). Material/Methods: A retrospective review was conducted from January 2000 to October 2024, identifying 49 patients with MFS who met the inclusion criteria: age ≥18 years, non-metastatic disease at diagnosis, and treatment with surgery and RT at our center. Data collected included surgical details, margin status, RT modality and dose, recurrences, and chemotherapy (CHT). Recurrence rates were estimated using the log-rank method. Results: The cohort consisted of 49 patients, predominantly male, with high-grade tumors primarily located in the lower limbs, classified as stage IIIA or IIIB (Table 1). Of these, 42.8% had prior resections at other institutions, and 30.6% underwent multiple resections.