(P 317) PROGNOSTIC FACTORS, CLINICAL AND TOXICITY OUTCOMES FROM A LARGE COHORT OF PATIENTS WITH SOFT TISSUE SARCOMA TREATED WITH PREOPERATIVE RADIATION THERAPY

Objective: Primary therapy for Soft Tissue Sarcoma (STS) often consists of a combined surgery and radiation therapy (RT). Preoperative RT may be advantageous due to lower dose requirements and possible tumor downstaging, particularly in association with chemotherapy (CT) and modern radiation techniques. This study evaluated efficacy, toxicity and prognostic-related features in STS patients treated with preoperative RT and surgery.

Methods: Clinical and treatment related data were collected from consecutive STS patients treated at our Institution with preoperative RT followed by surgery from 1991 to 2023. Overall survival (OS), Distant-metastasis free survival (DMFS), Local control (LC) data were collected and estimated using Kaplan-Meier method. Log-rank text and Cox model were conducted to identify factors related with outcome and toxicity.

Results: 156 patients, for whom follow-up data were available, were included in our analysis. Median age was 55 years. Tumors were mostly located in the limbs (94%). Disease stage was T>=3 in 71% of cases. Most represented histotypes were liposarcoma (LPS) (34%), undifferentiated pleomorphic sarcoma (UPS) (24%) and synovial sarcoma (5%).
RT prescription dose was 50 Gy in 25 daily fractions combined with CT in 82,5 % patients. IMRT was used in 34% of case.
R0 and R1 resection were obtained in 93% and 7% of patients respectively.
Severe surgical sequelae (wound dehiscence or sepsis) were reported in 16% of patients. Grade (G) 3 disease was observed in 69,8% patients. After a median follow-up of 32 months, OS rates at 2 and 5 years were 85% and 72%, DMFS rates were 69% and 57% and LC rates were 87% and 82%, respectively.
At multivariate analysis only R1 resection resulted significant for worse LC rates (p=0.0214), whereas G3 disease was correlated with worse DMFS (p=0.0029). At Cox analysis G3 (p=0.004), UPS (p=0.0028) and R1 (p=0.05) correlated with worse overall survival.
Use of IMRT and chemotherapy didn’t result in higher severe surgical sequelae.

Conclusion: In this large STS cohort, neoadjuvant treatment resulted in high RO rate and favorable outcomes. R1 resection and G3 disease correlated respectively with impaired LC and DM FS. Both factors were associated with poorer OS, highlighting the interest of treatment intensification. IMRT and concurrent CT were not correlated with surgical sequelae.