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.