Inclusion Criteria:  Patients who had cyclophosphamide treatment for immunosuppressant after allogeneic hematopoietic stem cell transplantation Patients age <19 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 a 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 Subjects who are pregnant or breast-feeding Subjects with psychiatric conditions that may interfere with the study Subjects who have a possibility of the disease getting worse as a treatment for clinical trials