Reduced-Intensity Conditioning in Allogeneic Stem Cell Transplantation for Hematological Malignancies: A Historical Perspective

Allogeneic hematopoietic stem cell transplantation represents a curative treatment approach for a large range of hematologic malignancies. Traditionally, high-dose radiochemotherapy as preparative regimen has been thought to be necessary for successful allogeneic stem cell transplantation. However, high-dose conditioning often results in considerable medullary and extramedullary toxicity, contributing to high rates of treatment-related mortality. This limits the use of this procedure to patients below 60 years of age without significant comorbidities. Since the peak incidence of most hematological malignancies is beyond the 5th decade of life, the majority of patients are not eligible for high-dose treatment. During the last 15 years, several dose-reduced or even non-myeloablative conditioning regimens have been developed, offering a curative treatment option for these patients. This review summarizes the history of reduced-intensity conditioning (RIC) transplantations, depicts the differences among regimens, highlights significant patient factors, and describes the impact on selected hematological malignancies.