A study conducted in patients with leukemia who underwent hematopoietic stem cell transplantation showed that carriers of CYP2B6*2A or CYP2B6*4 variant alleles treated with cyclophosphamide were at higher risk of developing hemorrhagic cystitis and oral mucositis, respectively (Rocha et al., 2009). The gene discussed is CYP2B6; the disease is leukemia.