Accelerated-phase (AP) myelofibrosis, currently defined by circulating blasts 10-19%, usually confers very high risk for progression and poor outcome. The outcome of hematopoietic stem cell transplantation for AP myelofibrosis has not been evaluated yet. We analyzed the outcome of 349 clinically and genetically annotated patients with primary or secondary myelofibrosis undergoing reduced intensity transplantation, of whom 35 had AP myelofibrosis. In comparison with chronic-phase (CP, <10% blasts), median leukocyte counts were higher, more patients had constitutional symptoms, and RAS mutations were detected more frequently in the AP group. After a median follow-up of 5.9 years, estimated 5-year overall survival was 65% (95% confidence interval, 49-81%) versus 64% (95% confidence interval, 59-69%) for the CP group (P=0.91), and median overall survival was not reached. In terms of relapse-free survival, estimated 5-year outcome for the AP group was 49% (95% confidence interval, 32-67%) versus 55% (95% confidence interval, 50-61%) for the CP group (P=0.65). Estimated 5-year non-relapse mortality was 20% (95% CI, 8-33%) for the AP group versus 30% (95% confidence interval, 24-35%; P=0.25) for the CP group. In terms of relapse, 5-year incidence was 30% (95% confidence interval, 14-46%) for the AP group versus 15% (95% confidence interval, 11-19%) for the CP group (P=0.02). Results were confirmed in multivariable analysis and propensity score matching. Increase in circulating blasts was associated with increased risk for relapse, showing strongest increase in risk for ≥10% blasts. In conclusion, reduced intensity transplantation showed excellent survival but higher relapse for AP myelofibrosis.
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