Inclusion Criteria:  children aged 2-12 years at the time of study entry with documented cancer scheduled to receive MEC or HEC (more than 30% emetogenic potential) with Karnofsky score of 60 or more (for patients aged greater than 10 years) or Lansky play performance score of 60 or more (for patients aged 10 years or less) predicted life expectancy of at least 3 months; and written informed consent provided by parent or guardian  Exclusion Criteria:  vomiting 24 hours before treatment day 1 known history of QT prolongation or allergic reaction to any of the study drugs symptomatic primary or metastatic CNS malignancy causing nausea or vomiting patients who received radiation therapy to the abdomen or pelvis in the week before treatment; active infection or any uncontrolled concurrent illness except for malignancy abnormal laboratory values at screening (peripheral absolute neutrophil count <1000 cells per μL, platelet count <100 000 cells per μL; alanine amino transferase or aspartate aminotransferase >5 times of the upper limit of normal for age, bilirubin or serum creatinine >1.5 times of the upper limit of normal for age) initiation of systemic corticosteroids within 72 hours before study drug administration or as part of the chemotherapy regimen; benzodiazepines or opioids initiated within 48 hours before treatment, except for single doses of triazolam, temazepam, or midazolam use of antiemetics within 48 hours of treatment use of CYP3A4 substrates or inhibitors within 7 days or CYP3A4 inducers within 30 days of treatment