CELECOXIB Plasma and Cerebral Spinal Fluid Pharmacokinetics in Children

Inclusion Criteria: Children aged 2-12 years, undergoing Maintenance phase chemotherapy for hematological malignancies and lymphomas (i.e. acute lymphoblastic leukemia \[ALL\] and lymphoblastic lymphomas \[LLy\] at CHEO. At this point, all patients would have achieved remission an average of 6 months earlier. Exclusion Criteria: 1. Age \< 2yrs and \>12yrs old 2. Children with non-hematologic malignancies 3. AML 4. Children undergoing a bone marrow aspiration (BMA) only 5. Serum creatinine \> 2 X UNL (upper normal limit) within 30 days 6. Abnormal liver function; alanine aminotransferase (ALT) \> 2 X UNL, Aspartate aminotransferase (AST) \> 2 X UNL, total \& direct bilirubin \> 2 X UNL within 30 days 7. History of peptic ulcer disease 8. Allergy to celecoxib or NSAIDs (note: sulpha allergy does not exclude celecoxib) 9. Recent (within 7 days) celecoxib ingestion 10. Patients receiving CYP2C9 inhibitors fluconazole, amiodarone, oxandrolone 11. Patients receiving CYP2C9 inducers rifampin and phenobarbitol 12. Patients receiving high (≥ 5 gm/m2) and/ or escalating doses of methotrexate. 13. Extremes of body mass index (BMI) (BMI \<5th percentile or \>95th percentile) 14. Parents of any participants, irrespective of age, who are unable to read and understand instructions relayed in English or French 15. Participant and/or parents of any participants, irrespective of age, who suffer from dementia, psychosis or any impairment that would prohibit the understanding and giving of informed consent or study-related reporting 16. Patient enrolled in another trial 17. Pregnancy.