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.

Inclusion Criteria: * Patients must have a histologically or cytologically confirmed malignant solid tumour. * Progression or recurrence of the tumour radiologically established or confirmed within the 4 weeks prior to inclusion. * Disease must be considered refractory to any line of conventional therapy or for which no effective conventional treatment exists. * Age: ≥4 to 21 years of age at study entry * Life expectancy: at least 8 weeks * ECOG Performance status ≤ 1 or Lansky-Play Scale ≥ 70% * Written informed consent of parent/guardian and patient assent * Wash out of 4 weeks in case of prior chemotherapy, 6 weeks if treatment included nitrosoureas, 2 weeks in case of vincristine alone; 6 weeks in case of prior radiotherapy (except palliative radiotherapy on non measurable lesions). * Patients must have recovered from the acute toxic effects of all prior therapy before enrolment into the study * Able to comply with scheduled follow-up and with management of toxicity * All patients with reproductive potential must practice an effective method of birth control while on study. * Female patients aged \> 12 years must have a negative pregnancy test within 7 days before study treatment. * Capable of swallowing oral medication Exclusion Criteria: * Pregnant and breast feeding women. * Uncontrolled intercurrent illness or active infection * Inability to swallow oral medication. * Patients on anticonvulsants will be allowed on study