Long-term outcome and relapse patterns in Ewing sarcoma patients with extensive lung/pleural metastases after a complete response to systemic therapy

Background Ewing sarcoma (ES) is sensitive to systemic therapy, including chemotherapy and anti-angiogenesis Tyrosine Kinase Inhibitors(aaTKIs). However, the prognosis of patients with metastatic disease remains poor. Recurrence or distant metastasis after a complete response (CR) or near-CR due to systemic therapy is not rare. Methods We reviewed data from 187 ES patients between 2014-2019 treated at a single institute in China. Patients with extensive lung/pleural metastases (L/Pmeta) who had a CR or near-CR after first- or second-line chemotherapy with or without aaTKIs were retrospectively enrolled. Event-free survival (EFS) and overall survival (OS) were determined using the Kaplan-Meier method. For patients who had L/P recurrence, images were reviewed to define the exact location of each recurrent lesion, compared with the primary L/P lesion before chemotherapy and summarized as the relapse pattern. Results Seventeen patients and 21 cases of CR/nCR (5 by VDC/IE, 3 by VIT, and 13 by AVI) were finally analyzed. Median follow-up for surviving patients was 39.6 (range, 14.5-60.9) months. Median EFS and OS were 9.3 (95% confidence interval [CI], 2.0-16.6) months and 37.5 (95% CI, 21.8-53.1) months, respectively. The 2-year EFS was 19% and the 2-year OS was 70.6%, respectively. Most patients (82.4%) received whole lung irradiation (WLI). Lung/pleural relapse occurred in 71.4% (15/21) of CR/nCR cases. Most notably, all recurrent lesions exactly coincided with the original metastatic lesions before chemotherapy (exactly in situ) in 9 of the 15 recurrent cases, which was thus the major relapse pattern, whereas 42.9% had distant metastases other than L/Pmeta. Conclusions Survival of ES patients with extensive L/Pmeta remains poor, even if they have a CR after systemic therapy. Recurrence exactly in situ is the major relapse pattern. WLI is not sufficient to prevent local recurrence in lung or pleura. More aggressive local treatment for metastatic lesions is warranted.