Phase I Dose Finding Study for Melatonin in Pediatric Oncology Patients With Relapsed Solid Tumors

Inclusion Criteria: * Patients must be able to take medication by mouth either by swallowing, chewing or sublingual routes. * Patients must have a documented life expectancy of ≥ 8 weeks. * Patients must have histologic or radiographic evidence of a relapsed malignant solid tumor. Intrinsic brain stem tumors or optic pathway gliomas may be diagnosed by clinical and radiologic methods. * Patient, parent, legal representative and/or guardian must sign a written informed consent. Assent, when appropriate, will be obtained according to institutional guidelines. * Minimum Weight Requirements: Dose level 1 - 22.2kg, Dose level 2 - 11.1kg, Dose level 3 - 5.6kg * Patients must be taking a stable dose (with no additions, modifications or deletions) of chemotherapy started ≥ 14 days prior study enrollment. * Prescribed Chemotherapy drug(s) must not be known to interact with melatonin * Adequate Bone Marrow Function Defined as: 1. Patients with solid tumors without bone marrow involvement: * Peripheral absolute neutrophil count (ANC) ≥ 1 x109/L * Platelet count ≥ 50 X 109/L (transfusion independent, defined as not receiving platelet transfusions within a 7 day period prior to enrollment) * Hemoglobin ≥ 80 g/L (may receive RBC transfusions) 2. Patients with known bone marrow metastatic disease are eligible for study but not evaluable for hematologic toxicity. * Must not be known to be refractory to red cell or platelet transfusions. * These patients do not need to meet the bone marrow function requirements, as hematological toxicity will not be measured due to metastatic disease. * Adequate Liver Function Defined as: * Total Bilirubin ≤ 1.5 x upper limit of normal (ULN) for age. * ALT ≤ 1.5 x ULN for age. Exclusion Criteria: * Chemotherapy: Melatonin inhibits the action of doxorubicin * Growth factors that support white cell number administered ≤ 7 days prior to enrollment. * Patients requiring corticosteroids who are not on a stable or decreasing dose of corticosteroid for ≥ 14 days. * Patients prescribed immunosuppressant therapy that is not specifically utilized for chemotherapy purposes. Patient prescribed: Cyclosporine, Mycophenolate Mofetil HCL, Tacrolimus, Sirolimus and Azathioprine should be excluded * Patients prescribed anti-coagulation therapy (Warfarin, Low Molecular Weight Heparin (LMWH), or System Heparin Therapy) * Concomitant medications that are known CYP1A2 inhibitors interact with Melatonin. * Patients prescribed megace, corticosteroids and periactin started ≤ 14 days prior to study enrollment. * Patients taking the following medications: benzodiazepines, nifedipine, NSAID's, ASA and/or Beta Blockers * Patients ≤ 7 days post-operative from any surgical procedure. * Patients with any signs of active post-operative bleeding. * Patients with an infection that is not responding to anti-microbial therapy. * Any condition that would negatively impact effective gut absorption and/or swallowing of study medication. * Patients in the opinion of the investigator may not be able to comply with study protocol requirements * Patients already receiving melatonin are excluded from the study. * Allergies to the medicinal and/or non-medicinal ingredients of melatonin which include: Melatonin, Calcium Salicate, Croscarmellose Sodium, IsoMalt, Magnesium Stearate, Microcrystalline Cellulose. * As melatonin can cause fatigue, patients taking melatonin should refrain from driving or operating machinery within 5 hours of taking the melatonin.