Posttransplant Cyclophosphamide‐Based Haploidentical Transplantation, With <scp>MMF</scp> 30 mg/kg, Compared With Unrelated Donor Transplantation With <scp>ATG</scp> 6 mg/kg, With Bone Marrow or Peripheral Blood Stem Cell Grafts

Several adaptations have been reported since the introduction of posttransplant cyclophosphamide (PTCy)-based haploidentical transplantation (Haplo). This single-center observational study compared the outcomes of PTCy-based Haplo with MMF at 30 mg/kg to a concurrent cohort of unrelated donors (URD) who received mainly ATG at 6 mg/kg proximal to transplantation. We included 174 patients (median follow-up: 33 months). Two-year OS for Haplo was 55%, which was not significantly lower than that for URD (67%, p = 0.22). Two-year RFS was 53% for Haplo, compared to 60% for URD (p = 0.31). Two-year GRFS was significantly worse for Haplo (24%) compared to URD (40%, p < 0.01). Relapse rates were similar (16% for Haplo and 21% for URD, p = 0.66), but non-relapse mortality was significantly higher for Haplo (31%) versus 19% for URD (p = 0.04). GVHD outcomes did not differ in univariable analyses. In multivariable analyses, there was a trend toward higher grades III-IV aGVHD (HR = 2.01, p = 0.08) and moderate to severe cGVHD (HR = 1.80, p = 0.05). In summary, we have shown that MMF at 30 mg/kg in Haplo transplants achieved similar PFS and OS compared to ATG-based URD. However, GRFS was lower, likely due to a significantly higher NRM associated with a trend towards higher moderate to severe cGVHD.