Comparison of Mycophenolate Mofetil and a Calcineurin Inhibitor Versus Calcineurin Inhibitor Based Graft-Versus-Host-Disease Prophylaxis for Matched Unrelated Donor Transplant for Acute Myeloid Leukemia. a Study from the ALWP of the EBMT

Cyclosporine A (CsA) alone or in combination with mycophenolate mofetil (MMF) has been used as graft-versus-host-disease (GvHD) prophylaxis since the early development of reduced intensity conditioning (RIC). The association of CsA+MMF, while commonly used after transplantation from a matched unrelated donor (MUD), has never been tested in a large randomized prospective trial.

We retrospectively investigated the outcomes of adult patients with AML in complete remission (CR) undergoing a MUD transplant using CsA+MMF or CsA alone as GvHD prophylaxis, transplanted between 2007-2017 and registered with the ALWP of the EBMT.

Of the 497 patients who were evaluated, 183 received CsA alone and 314 received CsA+MMF. The median age at transplant was similar, being 59 (range, 20-75) years in the CsA group and 60 (range, 21-75) years in the CsA+MMF group. All patients underwent a RIC regimen with fludarabine and busulfan and received anti-thymocyte globulin as part of the conditioning. The median follow-up was 33 (range, 18-60) months in the CsA group and 34 (range, 18-75) months in the CsA+MMF group. Disease status at transplant was first complete remission (CR1) for 81% (n=149) in CsA group and 86% (n=268) in CsA+MMF group (p=NS). Poor risk cytogenetics was reported for 19% of patients who received GvHD prophylaxis with CsA alone and for 15% of patients receiving CsA+MMF (p=NS). Peripheral blood stem cells (PBSC) was the graft source in 93% of patients receiving CsA alone and in 96% of patients who received CsA+MMF (p=0.17). Female to male mismatch was present in 13% and 15% of patients in the CsA goup and CsA+MMF group respectively, (p=NS). All but 2 patients engrafted. The 100 day cumulative incidence (CI) of grade II-IV and grade III-IV GvHD were 30% and 10%, respectively. The 2-year CI chronic GvHD was 35% and CI of extensive cGvHD was 15%. The 2-year CI of non-relapse mortality (NRM) and relapse were 19% and 25%, respectively. Of the 81 patients who died in the CsA group, disease recurrence (n=31), GvHD (n=20) and infection (n=17) were the most common causes of death. One hundred twenty seven patients died in the CsA+MMF group; cause of death was relapse for 53, GvHD for 28 and infection for 28 of them. The 2-year GVHD-free relapse-free survival (GRFS), leukemia- free survival (LFS), and overall survival (OS) were 45%, 56% and 60%, respectively.

On multivariate analysis (MVA), no statistically significant differences were found among the two GvHD prophylaxis groups with respect to relapse, NRM, LFS, OS, acute and chronic GvHD.

A positive cytomegalovirus serology of the donor was associated with higher NRM [HR=2.03, p<0.001] and higher cGvHD [HR=1.44, p=0.03] and a lower OS [HR 1.66, p<0.001], LFS [HR=1.69, p=0.001] and GRFS [HR=1.75, p<0.001].

In a subgroup analysis of patients in CR1 who received PBSC, (CsA alone, n=138; CsA+MMF, n=257), no differences were detected between the two groups for relapse, NRM, LFS, OS, or aGvHD, but patients who received CsA alone tended to have a higher cGvHD (41% vs 33%, p=0.05). However, on MVA, although the risk of cGvHD was lower in the CsA+MMF group, this finding was not statistically significant [HR=0.67, p=0.08]. Adverse cytogenetics was an independent risk factor for relapse [HR=2.22, p<0.001].

In this study, we observed comparable outcomes in patients with AML in CR1 who underwent MUD transplantation and RIC with CsA+MMF or CsA alone as GvHD prophylaxis. This suggests that both strategies may be considered valid approaches. Additional randomized trials are needed to further assess which patients could benefit from the addition of MMF in GvHD prophylaxis.