[1] Hosp Sick Children, Div Haematol Oncol, Toronto, ON M5G 1X8, Canada
[2] Hosp Sick Children, Program Child Hlth Evaluat Sci, Toronto, ON M5G 1X8, Canada
[3] Hosp Nacl Ninos Benjamin Bloom, San Salvador, El Salvador
[4] Unidad Nacl Oncol Pediat, Guatemala City, Guatemala
[5] Hosp Escuela Tegucigalpa, Tegucigalpa, Honduras
[6] St Jude Childrens Res Hosp, Memphis, TN 38105 USA