8505 Background: In the largest adjuvant phase III study in stage II melanoma to date, EORTC 18961 assessed the efficacy and toxicity of ganglioside GM2-KLH/QS-21 vaccination versus observation (OBS). Methods: Patients (Pts) were observed or received vaccine sc once weekly weeks 1-4, every 3 months from week 12 for first 2 years and every 6 months during third year (total of 14 vaccinations). Stratification factors at randomization were: Breslow thickness, ulceration, being staged yes vs no by sentinel node or elective lymph node dissection, sex and institution. Relapse-free survival (RFS) was the prespecified primary endpoint; distant metastasis-free survival (DMFS) and overall survival (OS) were secondary endpoints. An intent-to-treat analysis was performed. Results: Between March 2002 and December 2005, 1,314 pts entered the trial. Patient demographics showed excellent balance for prognostic factors. The second interim analysis was performed when 267 RFS events were reported. For the primary endpoint, ...