A Clinical Trial Using Metronomic Oral Low-dose Cyclophosphamide Alternating With Low-dose Oral Methotrexate With Continuous Celecoxib and Weekly Vinblastine in Children and Adolescents With Relapsed or Progressing solid Tumours. (SFCE METRO 01) Sponsor: Assistance Publique Hopitaux De Marseille Purpose To establish the anti-tumour effect of this metronomic combination regimen defined by progression-free survival (PFS) after two cycles of treatment (4 months) and 12 months of treatment, (...)