The effects of substituting cladribine for fludarabine on outcomes of a reduced intensity conditioning regimen.

Abstract

e18518 Background: Drug shortages may be encountered especially in times of pandemics and war. The extrapolation of data focusing on different diseases may provide clinical clues for substituting two chemotherapeutic drugs of the same class. The substitution of cladribine for fludarabine in a reduced intensity conditioning (RIC) regimen composed of fludarabine, melphalan and total body irradiation (TBI) may yield similar side effect profile and outcomes. Methods: Consecutive patients undergoing an allogeneic stem cell transplant in our center between November 2019 to December 2022 were included. Within this period cladribine had to be substituted for fludarabine during a drug shortage. All patients received intravenous melphalan 75 mg/m2/day on day -2, and 200 cGy TBI on day -1. The regimen included either subcutaneous cladribine 10 mg/m2/day on days -5 to -2, or intravenous fludarabine 40 mg/m2/day on days -5 to -2. Graft versus host disease (GvHD) prophylaxis included a calcineurin inhibitor (CNI) + mycophenolate mofetil (MMF) for matched related donor transplants; and post-transplant cyclophosphamide + CNI + MMF for matched unrelated (MUD) and haploidentical donors. The distributions and medians of studied parameters in two cohorts were compared with non-parametric methods. Overall survival (OS), progression-free survival (PFS) and transplant-related mortality (TRM) were estimated by the Kaplan-Meier Method. The cut-off for statistical significance was defined as p<0.05. Results: A total of 70 patients (27 in cladribine and 43 in fludarabine cohort) were included. Median age was 59 (22 to 76) and 64.3% constituted males. Median follow-up was 10.2 months (0.1 to 44.7). Acute leukemia diagnosis, intermediate to high disease risk index (DRI) and intermediate to high Charlson comorbidity index (CCI) constituted 45.7%, 60.0% and 58.1% respectively. Haploidentical donors were used in 28.6%. The distribution of gender, diagnosis, DRI and CCI scores, donor type, total CD34 dose given, panel reactive antibody (PRA) positivity were similar. Median days to neutrophil engraftment was shorter with fludarabine (19 vs 16, p=0.01), however, median duration of in-unit stay was similar (27 vs 28 days, p=0.73). TRM, nausea and acute GvHD frequency was lower with cladribine (p=0.35, p=0.001 and p=0.02, respectively). Typhilitis and perianal infections were more common with cladribine (p=0.07 and p=0.04, respectively). OS and PFS were similar (p=0.81 and p=0.66, respectively). When cladribine was compared to fludarabine on day +90, OS was 78,0% (95% CI: 62.3-93.7) vs 65,0% (95% CI: 51.3-78.7); PFS was 70.0% (95% CI: 52.4-87.6) vs 65.0% (95% CI: 51.3-78.7); TRM was 19.0% (95% CI: 3.3-34.7) vs 24.0% (95% CI: 10.3-37.7). Conclusions: Cladribine may be safely constituted for cladribine in a RIC regimen and may yield similar, even some favorable, outcomes when compared to fludarabine.