Inclusion Criteria:  Patients who had mycophenolate treatment at least 3 days for immunosuppressant after allogenic hematopoietic stem cell transplantation Patients age <18 years Written Study Informed consent and/or assent from the patient, parent, or guardian  Exclusion Criteria:  Known hypersensitivity to mycophenolate mofetil or similar class of drug substance Patients in medically critical condition such as severe infection or unstable vital signs Any condition that would, in the Investigator's judgment, interfere with full participation in the study Patients with hypoxanthine-guanine phosphoribosyltransferase deficiency(HGPRT) such as Lesch-Nyhan or Kelley-Seegmiller syndrome)