Can doses of post-transplantation cyclophosphamide in haploidentical stem cell allografts be reduced?

Allogeneic hematopoietic stem cell transplantation (HSCT) remains the most important curative modality for several hematologic malignancies, but an HLA-matched sibling or unrelated donor is not always available, particularly for ethnic minorities and multiethnic families. We have shown that Haplo-HSCT can be conducted safely on an outpatient basis, using peripheral blood stem cells; this leading into substantial decreases in the costs. In this study twenty-one patients prospectively received the conventional dose of post-transplantation cyclophosphamide (PTCy): (50 mg/Kg on days 3 and 4), whereas 10 were given reduced doses of the drug (25 mg/Kg on days 3 and 4). According to the statistical analysis, the two comparative groups (PTCy 50 mg/kg vs PTCy 25 mg/kg) had no significant difference in terms of age, sex, hematological recovery, and type of conditioning regimen. The median OS for the group PTCy 50 mg/kg is 5.7 months meanwhile for the group PTCy 25 mg/kg the median is 6.4 months. The median follow up for entire group is 4.5 months (IQR: 1.1-18.9 mo). These results could indicate that the Cy-dependent hematological toxicity can be reduced without compromising its effectivity. This preliminary observation may be considered as an idea to conduct prospective randomized studies to explore the possibility of significantly reducing the doses of PT-Cy in the setting of Haplo-HSCT. ClinicalTrials.gov identifier: NCT05780554.