(P 443) SURGICAL RESECTION OF EXTREMITY EWING'S SARCOMA BASED ON POST-CHEMOTHERAPY TUMOUR VOLUME RESULTS IN SAFE MARGINS

Objective: Neoadjuvant chemotherapy is an integral part of the multimodal treatment approach to Ewing’s Sarcoma. While chemotherapy may help reduce the tumour volume, the consensus amongst clinicians is that the entire pre-treatment tumour volume should still be resected during surgery to account for any residual, viable, and infiltrative malignant cells. However, this can lead to increased surgical morbidity and functional deficits. Therefore, this study investigated the safety of performing surgical resection for Ewing’s Sarcoma based on post-chemotherapy tumour volumes.

Methods: A single centre retrospective review from a prospectively collected database between 1989 and 2019 was performed. All patients who underwent limb salvage resection of Ewing’s sarcoma were included. Patients who underwent radiation therapy or initially presented with local recurrence were excluded. Outcomes of interest were surgical margins along with local recurrence-free and metastatic disease-free intervals, and overall survival. Survival analysis was performed using the Kaplan-Meier technique. A Cox-Regression analysis was performed to identify independent variables that affected the survival analysis.

Results: All 40 patients who were eligible for analysis underwent limb salvage resection based on post-chemotherapy MRI (magnetic resonance imaging) planning. The mean age was 26 years (range 13 to 64 years) with 17 males and 23 females. Tumour locations included the femur (n=19), tibia (n=8), scapula (n=5), humerus (n=5), fibula (n=2), and ulna (n=1). Four patients initially presented with pathologic fracture and four with metastatic disease. Tumour size decreased following chemotherapy in 82% of patients and increased in 18%. Tumour necrosis ≥ 90% was observed in 55% of patients. Twenty-five patients underwent additional postoperative chemotherapy. Complications were observed in 25% of patients including superficial wound infection (n=3), deep infection requiring debridement (n=1), nerve palsy (n=2), allograft fracture (n=1), acute soft tissue flap reconstruction failure (n=1), endoprosthesis bushing wear (n=2).
The mean final follow-up was 87 months (range two to 328 months). Surgical margins were negative in all but one patient who had micro-positive margins. Local recurrence was seen in three of 40 patients (8%). Eight of 36 (22%) patients, who initially presented with isolated disease, developed metastatic disease. The five-year local recurrence-free, metastatic disease-free, and overall survival was 91.1%, 75.5%, and 71.8% respectively. Patient age, sex, tumour location, tumour size, response to chemotherapy, and pathologic fracture were not statistically significant for outcomes in the multivariate analysis.

Conclusion: The results suggest that the resection of extremity Ewing’s sarcoma based on post-chemotherapy tumour volume results in an oncologic outcome comparable to those based on pre-chemotherapy tumour volume. Although further prospective comparative studies are required, the current findings suggest safe surgical margins can be achieved with this approach, potentially allowing for improved soft tissue coverage and functional outcomes.