CAST Regimen for GvHD Prophylaxis: A CIBMTR Propensity Score-Matched Analysis

Previously, we reported excellent results with the combination of post-transplant cyclophosphamide (PTCy), abatacept, and a short course of tacrolimus (CAST) for the prevention of graft-versus-host disease (GvHD) following peripheral blood haploidentical transplantation. To further substantiate these results, we performed a propensity score-matched analysis. Patients enrolled in the CAST trial were matched with patients from a contemporaneous cohort from the Center for International Blood and Marrow Transplant Research database who received PTCy, tacrolimus, and mycophenolate mofetil, using nearest neighbor propensity score matching. An excellent balance between pairs was achieved as measured by the density distribution and standardized differences of covariates (median 0.09). The rates of acute GvHD grades II to IV at day +120 and 1-year GvHD- and relapse-free survival were 16.7% and 66.7% in the CAST cohort versus 28.6% and 47.6% in the control group, respectively. This trend did not reach statistical significance (P =.14 and.07), possibly due to the small numbers of patients and events. On the other hand, CAST was associated with a statistically significant reduction in the incidence of relapse (9.5% versus 26.2%, P =.045) with improved disease-free survival (85.7% versus 61.9%, P =.01). Our data provides a strong impetus to examine CAST in a randomized clinical trial.