Outcomes of allogeneic hematopoietic stem cell transplantation in patients with blast phase myelofibrosis: molecular signature and intensive chemotherapy matter.

Patients with blast-phase (BP) myeloproliferative neoplasms have dismal outcomes, but allogeneic hematopoietic stem cell transplantation (alloHSCT) may offer a potential cure. However, the optimal pre-transplant blast-reduction therapy remains to be determined. We retrospectively analyzed outcomes in a molecularly annotated cohort of 24 patients with BP myelofibrosis (MF) who underwent alloHSCT between 2008 and 2023. Before conditioning, 20 patients received intensive induction chemotherapy, 1 received decitabine plus venetoclax, and 3 proceeded directly to transplant. At transplantation, 13 patients (54%) were in complete remission (CR), defined as bone marrow blast < 5%, or CR with incomplete count recovery (CRi), while 11 (46%) had active disease. The median follow-up was 2.9 years (range 0.02-15.5). The 3-year overall survival (OS) was 62%, progression-free survival (PFS) was 49%, relapse incidence was 38%, and non-relapse mortality was 12%. There was a trend toward better OS and PFS in patients transplanted in CR/CRi compared with those with active disease (OS 68% vs. 55%, HR 0.42, p = 0.16; PFS 61% vs. 36%, HR 0.49, p = 0.21). Mutations in TP53 and EZH2 were associated with significantly inferior PFS (HR 6.28, p = 0.008 for TP53 and HR 3.8, p = 0.04 for EZH2).Compared with a historical cohort of 50 patients transplanted during the same period for chronic-phase MF, outcomes were similar (3-year OS: 62% vs. 58%; p = 0.6181). In conclusion, our results suggest that achieving remission before alloHSCT in BP-MF is associated with favorable outcomes. The adverse impact of TP53 or EZH2 mutations supports early post-transplant strategies to prevent relapse.