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