The purpose of this study is to examine the pharmacokinetics (PK) of melphalan in children
undergoing hematopoietic stem cell transplantation (HSCT). Melphalan is an important
component of HSCT preparative regimens, but can be associated with significant toxicity. PK
data is a powerful clinical tool that, when used to develop individualized treatment plans
for a specific patient, may ultimately increase the likelihood of selecting the right dose
for the right patient and/or of reducing the number of adverse drug events. The
investigators' goal is to establish baseline pediatric melphalan PK data. These data may be
used for patient specific dosing of melphalan in the future to minimize toxicity and improve
transplant outcomes.