Results of the Latin American Pediatric Oncology Group (GALOP-2011) Trial for Patients With Localized Ewing Sarcoma: A Multicentric Study of Interval-Compressed Multiagent Chemotherapy.

Background: GALOP investigators developed a prospective cooperative protocol for localized Ewing sarcoma (ES) incorporating interval-compressed chemotherapy (VDC/IE, vincristine, doxorubicin, cyclophosphamide/ifosfamide and etoposide). After completing conventional treatment, patients were randomized to 1 year of metronomic chemotherapy (vinblastine and cyclophosphamide).

Methods: Phase III randomized prospective trial. Induction consisted of six alternating cycles of VDC/IE every 14 days, followed by local control, and eight cycles of consolidation every 21 days. After consolidation, patients were randomized 1:1 to metronomic chemotherapy or stop treatment, balanced by age (>/< 14 years-old), sex (M/F), site (pelvic/non-pelvic), and size (>/< 8 cm). The results of randomization will be published elsewhere with longer follow-up.

Results: Between 2011 and 2019, 315 patients (59.7% male, median age 11.0 years) were recruited across 34 centers in Argentina, Brazil, Chile, and Uruguay. The most frequent localizations were axial (45.1%), extremity (38.1%), and pelvic (16.8%). The median time interval between cycles was 19 and 22 days at induction and consolidation, respectively. There were no unexpected toxicity or toxic deaths related to interval compression. The overall response rate post-induction was 81.6%. Local treatment with surgery (50.8%), radiotherapy (19.7%), or a combination (26%) was performed in 304 (96.5%) patients. With a median follow-up of 50 months (range: 1.67-121.7), the 5-year overall and event-free survivals were 68.6% (SE: 0.030) and 63.7% (SE: 0.029), respectively.

Conclusion: Implementation of a multi-institutional protocol with the strategy of interval-compressed induction for ES in South America was feasible with favorable results. This success is attributed to rigorous protocol adherence, extensive educational efforts, and a strong emphasis on data quality maintenance, demonstrating a reproducible model for countries with similar resource limitations.