- Ages =< 50 years of age with hematologic diseases treatable by allogeneic HCT who through pre-existing medical conditions or prior therapy are considered to be at high risk for regimen related toxicity associated with a high dose transplant (> 40% risk of transplant related mortality [TRM]); this criterion can include patients with a hematopoietic cell transplant-comorbidity index (HCT-CI) score of > 3; transplants should be approved for these inclusion criteria by the principal investigators at the collaborating centers and at Fred Hutchinson Cancer Research Center (FHCRC); all children < 12 years must be discussed with the FHCRC principal investigator (PI) prior to registration