Introduction
Many studies of conditioning regimens for hematopoietic cell transplantation (HCT) have been conducted over the last few decades, and various regimens are now available. Furthermore, conditioning intensity and its effects on transplantation outcomes have been well researched, which has led to decreased transplantation-associated morbidity and mortality [1-4]. Several studies have revealed the equivalence of a reduced intensity regimen, in terms of overall survival (OS) and event-free survival (EFS), in comparison to a conventional myeloablative conditioning (MAC) regimen [5-8]. Additionally, the incidence of graft-versus-host disease (GVHD) is known to be affected by conditioning intensity [9-13]. However, there are no reports concerning the relationship between clinical outcomes and differences in scheduling strategies for conditioning regimens consisting of equivalent doses and types of chemotherapeutic agents and total body irradiation (TBI).
Conditioning regimens for HCT should be performed according to the usual standards and timescales. Nonetheless, one- or two-day intervals are occasionally enacted during the conditioning period because of hospital closure, predetermined dates of unrelated donor HCT, or simultaneous HCTs for multiple patients. Furthermore, unexpected situations requiring HCT postponement can occur. Therefore, it is important to identify potential negative effects of HCT conditioning interruptions on clinical outcomes. We evaluated this hypothesis in pediatric patients with oncologic diseases undergoing HCT after MAC.