Low-Dose Total Body Irradiation Added to Fludarabine and Busulfan Reduced-Intensity Conditioning Reduces Graft Failure in Patients with Myelofibrosis.

Allogeneic hematopoietic cell transplantation (alloHCT) is indicated for patients with intermediate-risk or high-risk myelofibrosis (MF) and remains the sole potential cure. Reduced-intensity conditioning (RIC) is commonly used because of older patient age, comorbidities, and a high incidence of transplantation-related mortality. Patients with MF are at increased risk of graft failure (GF), which is more common with RIC regimens, and is associated with shortened overall survival (OS). Owing to the high rate of GF with conventional fludarabine (Flu) and busulfan (Bu) RIC, we added low-dose total body irradiation (TBI; 200 cGy) for patients with MF. We retrospectively compared alloHCT outcomes in adult patients with MF who received RIC with Flu/Bu/TBI and those who received RIC with Flu/Bu. The primary endpoint was the incidence of GF. Secondary endpoints included time to engraftment, acute and chronic graft-versus-host disease (GVHD), hepatic sinusoidal obstruction syndrome (SOS), nonrelapse mortality, overall response rate, progression-free survival, and OS. Of 33 patients who underwent alloHCT, 8 received Flu/Bu RIC and 25 received Flu/Bu/TBI RIC. GF occurred in 50% of the Flu/Bu recipients (all secondary GF) and in 4% of the Flu/Bu/TBI recipients (1 case of primary GF; relative risk, .08; 95% confidence interval [CI], .01 to .62; P = .0016). GF incidence was similar with related or unrelated donors and in patients who did and did not receive Janus-associated kinase inhibitors prior to alloHCT. Molecular remission and donor chimerism ≥99% were significantly more common with Flu/Bu/TBI. No significant differences in acute GVHD, chronic GVHD, or time to engraftment were observed. SOS occurred in none of the 8 patients who received Flu/Bu and in 6 of the 25 patients who received Flu/Bu/TBI, but this difference did not reach statistical significance. Progression or relapse at 1 year was less common with Flu/Bu/TBI (0% versus 63%; P < .001). The median OS was 49 months for Flu/Bu/TBI recipients and 30.8 months for Flu/Bu recipients (hazard ratio, .98; 95% CI, .33 to 2.88; P = .97). Flu/Bu/TBI resulted in a significant reduction in GF and a significant improvement in the frequency of molecular remission and full donor chimerism compared with Flu/Bu. The addition of low-dose TBI to Flu/Bu successfully mitigates against GF in patients with MF without increased rates of complications.