Busulfan (Bu)-containing regimens are commonly used in myeloablative conditioning regimens before allogeneic hematopoietic cell transplantation (HCT). Yet, there is considerable variability on how Bu is administered related to frequency (4 times a day [Q6] or daily [Q24]) and combinations with other chemotherapeutic agents (cyclophosphamide [Cy] or fludarabine [Flu]). We performed a prospective cohort study of recipients of Bu-based conditioning according to contemporary practices to compare different approaches (BuCy Q6, n = 495; BuFlu Q24, n = 331; BuCy Q24, n = 96; BuFlu Q6, n = 91) in patients with myeloid malignancies between 2009 and 2011. BuFlu Q24 recipients were more likely to be older and tended to have worse performance status and a higher comorbid burden. The cumulative incidences of hepatic veno-occlusive disease (P = .40), idiopathic pneumonia (P = .50), and seizures (P = .50) did not differ across groups. One-year HCT-related mortality ranged from 12% to 16% (P = .80), 3-year relapse incidence ranged from 32% to 36% (P = .80), and 3-year overall survival ranged from 51% to 58% (P = .20) across groups. This study demonstrates that HCT conditioning regimens using i.v. Bu Q6 or Q24 alone or in combination with Cy or Flu have similar outcomes in the myeloablative setting for treatment of myeloid malignancies.
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