Rapid regression of bone marrow fibrosis after dose-reduced allogeneic stem cell transplantation in patients with primary myelofibrosis

Objective To investigate the effect of a busulfan/fludarabine-based reduced intensity conditioning followed by allogeneic stem cell transplantation on regression of bone marrow fibrosis in patients with myelofibrosis. Methods Twenty-four patients (male, n = 16; female, n = 8) with a median age of 52 years (range, 32–63 years) were included. Six patients were transplanted from human leukocyte antigen–identical siblings and 18 patients from matched unrelated donors. Diagnosis was primary myelofibrosis in 18 patients and secondary myelofibrosis in 6 patients; in 4 of them, primary myelofibrosis evolved from polycythemia vera, and in 2 of them from essential thrombocythemia. Using the European Consensus on grading bone marrow fibrosis, all patients had advanced marrow fibrosis MF-2 (n = 13) or MF-3 (n = 11) before allografting According to the Lille Risk Factor Scoring System, patients were classified as low risk (n = 5), intermediate risk (n = 16), or high risk (n = 3). Results After stem cell transplantation, a complete (MF-0) or nearly complete (MF-1) regression of bone marrow fibrosis was seen in 59% at day +100, in 90% at day +180, and in 100% at day +360. No correlation between occurrence of acute graft-vs-host disease and fibrosis regression on day +180 was observed. Conclusion This study shows that allogeneic stem cell transplantation after reduced-intensity conditioning resulted in rapid regression of bone-marrow fibrosis.