This is a prospective, randomized, open label, parallel-group, multicenter phase III study to evaluate the efficacy and safety of active specific immunotherapy with racotumomab plus best supportive care versus best supportive care in patients with advanced NSCLC who have achieved an Objective Response (Partial or Complete Response) or Stable Disease with standard first-line treatment. Also immunological parameters will be evaluated. Best supportive therapy will be administered to all patients in the study according to institutional standards and includes any subsequent onco-specific therapies. 1082 patients will be included in the study, with non-small cell lung cancer in stages IIIA (non-resectable), IIIB or IV.