Genetic factors rather than blast reduction determine outcomes of allogeneic HCT in BCR-ABL-negative MPN in blast phase

There is a limited understanding of the clinical and molecular factors associated with outcomes of hematopoietic cell transplantation (HCT) in patients with BCR-ABL-negative myeloproliferative neoplasms in blast phase (MPN-BP). Using the Center for International Blood and Marrow Transplant Research database, we evaluated HCT outcomes in 177 patients with MPN-BP. Ninety-five (54%) had sufficient DNA for targeted next-generation sequencing of 49 genes clinically relevant in hematologic malignancies. At 5 years, overall survival (OS), cumulative incidence of relapse, and nonrelapse mortality of the study cohort was 18%, 61%, and 25%, respectively. In a multivariable model, poor-risk cytogenetics was associated with inferior OS (hazard ratio [HR], 1.71; 95% CI, 1.21-2.41) due to increased relapse (HR, 1.93; 95% CI, 1.32-2.82). Transplants using mobilized peripheral blood (PB) were associated with better OS (HR, 0.60; 95% CI, 0.38-0.96). No difference in outcomes was observed in patients undergoing HCT with PB/BM blasts <5% vs those with active leukemia. Among the 95 patients with molecular data, mutation of TP53, present in 23%, was the only genetic alteration associated with outcomes. In a multivariate model, TP53-mutant patients had inferior OS (HR, 1.99; 95% CI, 1.14-3.49) and increased incidence of relapse (HR, 2.59; 95% CI, 1.41-4.74). There were no differences in the spectrum of gene mutations, number of mutations, or variant allele frequency between patients undergoing HCT with PB/BM blasts <5% vs those with active leukemia. Genetic factors, namely cytogenetic alterations and TP53 mutation status, rather than degree of cytoreduction predict outcomes of HCT in MPN-BP. No meaningful benefit of conventional HCT was observed in patients with MPN-BP and mutated TP53.