Survival Outcomes in Metastatic Ewing Sarcoma Treated With Whole-Lung Radiation

Background and objective There is a scarcity of research on outcomes in patients with metastatic Ewing sarcoma limited to pulmonary metastases who receive whole-lung radiotherapy (WLRT). In light of this, this study aimed to evaluate the use of WLRT and compare the survival outcomes between patients with metastatic Ewing sarcoma who received treatment with WLRT and those who did not. Materials and methods Patients of all ages with metastatic Ewing sarcoma restricted to the lung who were referred to the British Columbia (BC) Cancer from 1995 to 2017 were identified from the Sarcoma Outcomes Unit (SARCOU). Patient demographics and tumor and treatment characteristics were compared between cohorts treated with WLRT versus those who did not undergo WLRT. Five-year progression-free survival (PFS) and overall survival (OS) were evaluated using Kaplan-Meier (KM) estimates and compared between treatment groups with log-rank tests. Results The study cohort comprised 30 patients (median follow-up time: 6.8 years). Overall, the median age of the patients was 16 years (range: 4-86 years) and 60% were female; the primary disease sites were as follows: 27% axial skeleton, 53% appendicular skeleton, 20% visceral, 86% had ≥2 lung metastases, and 60% had bilateral disease. Fifteen (50%) patients received WLRT (median of 1500 cGy in 10 fractions). Chemotherapy was used in 97% of patients. The rate of surgery for lung metastases was 40%, which was similar between the WLRT and non-WLRT groups. The median size of the largest lung metastasis in the WLRT cohort was 1 cm (range: 0.3-1.8 cm), compared to 2 cm (range 0.5-6.7 cm) in the non-WLRT cohort (p=0.05). Demographics and tumor characteristics were otherwise not significantly different between the two treatment groups (all p>0.05). Among patients who received WLRT, 53% had complete response (CR), 7% partial response (PR), and 40% had disease progression. The five-year PFS was 86% vs. 59% (p=0.33) and OS was 78% vs. 54% (p=0.24) respectively for patients in the WLRT group vs. those in the non-WLRT group. The five-year PFS outcomes were higher on univariate analysis in patients with appendicular skeletal compared to axial skeletal and visceral primary sites (87.5% vs. 58% vs. 50%, respectively, p=0.02) and in patients with the size of the largest lung metastasis <2 cm vs. those with a size ≥2 cm (80% vs. 25%, p=0.04). Conclusions Patients treated with WLRT had a smaller-volume lung disease and over half of the patients who received WLRT had either complete or partial response. Trends of improved PFS and OS at five years were observed among patients who received WLRT compared to the non-WLRT group, but these were not statistically significant.