In conclusion, the patients’ CYP2B6 metabolizing capacity appeared to significantly influence the development of severe hematologic toxicity related to lymphopenia, thrombocytopenia and monocytopenia induced by the therapy, whereas no effect of CYP2B6 function on the reduction of neutrophils, eosinophils and red blood cells was observed in neuroblastoma patients. Here, CYP2B6 is linked to lymphopenia.