CYP2B6 and Decreased total neutrophil count: Severe (grade 3 and grade 4) hematologic toxicity (leukocytopenia, and neutropenia) was observed in more than half of the adult Japanese cancer patients treated with cyclophosphamide, and grade 4 toxicity was associated with high 4-hydroxycyclophosphamide exposure and CYP2B6 polymorphisms33.