Between December 1 , 2006 , and February 24 , 2012 , a total of 224 patients 1 to 21 years of age with hematologic cancer were randomly assigned to undergo double-unit ( 111 patients ) or single-unit ( 113 patients ) cord-blood transplantation after a uniform myeloablative conditioning regimen and immunoprophylaxis for graft-versus-host disease ( GVHD ) .