Comorbidities and hematopoietic cell transplantation outcomes.

Conventional allogeneic hematopoietic cell transplantation (allo-HCT) is a potentially curative treatment option for various hematological diseases due, in part to high-dose conditioning and, in part, to graft-versus-tumor effects. Reduced-intensity or non-myeloablative conditioning regimens have relied mostly on graft-versus-tumor effects for disease control, and their advent has allowed relatively older and medically infirm patients to be offered allo-HCT. However, both HCT modalities have been associated with organ toxicities and graft-versus-host disease, resulting in substantial non-relapse mortality. It has become increasingly important to optimize pre-transplant risk assessment in order to improve HCT decision making and clinical trial assignments. Single-organ comorbidity involving liver, lung, heart, or kidney before HCT has been traditionally found to cause organ toxicity after HCT. Recent efforts have resulted in the advent of a weighted scoring system that could sensitively capture multiple-organ comorbidities prior to HCT. The HCT-comorbidity index (HCT-CI) has provided better prediction of HCT-related morbidity and mortality than other non-HCT-specific indices. Subsequent studies, with the exception of a few studies with modest numbers of patients, have confirmed the prognostic importance of the HCT-CI. Further, the HCT-CI has been consolidated with various disease-specific and patient-specific risk factors to refine assignments of patients to the appropriate HCT setting. Ongoing studies are addressing prospective validation of the HCT-CI, furthering our understanding of biological aging, and enhancing the applicability of the HCT-CI comorbidity coding. Future knowledge of the impacts of multiple comorbidities on post-HCT toxicities might guide new prophylactic and therapeutic interventions to lessen the procedure's mortality.