Clearance of Driver Mutations after Transplantation for Myelofibrosis.

Abstract

Allogeneic hematopoietic stem-cell transplantation is the only curative treatment for myelofibrosis. Driver mutations are the pathophysiological hallmark of the disease, but the role of mutation clearance after transplantation is unclear. We used highly sensitive polymerase-chain-reaction technology to analyze the dynamics of driver mutations in peripheral-blood samples from 324 patients with myelofibrosis (73% with <i>JAK2</i> mutations, 23% with <i>CALR</i> mutations, and 4% with <i>MPL</i> mutations) who were undergoing transplantation after reduced-intensity conditioning. Mutations were detected before transplantation and at 30, 100, and 180 days after transplantation to measure clearance and its effect on relapse and cure. The two primary end points were relapse and disease-free survival. At day 30 after transplantation, mutation clearance was found in 42% of the patients who had <i>JAK2</i> mutations, 73% of those who had <i>CALR</i> mutations, and 54% of those who had <i>MPL</i> mutations; the corresponding percentages at day 100 were 63%, 82%, and 100%. The cumulative incidence of relapse at 1 year was 6% (95% confidence interval [CI], 2 to 10) among patients with mutation clearance at day 30 after transplantation and 21% (95% CI, 15 to 27) among those without mutation clearance at day 30. Disease-free and overall survival at 6 years were 61% and 74%, respectively, among patients with mutation clearance at day 30 after transplantation and 41% and 60%, respectively, among those without mutation clearance at day 30. Mutation clearance at day 30 appeared to outperform traditional donor chimerism as a measure of response; it was independently associated with a reduced risk of relapse or progression (hazard ratio, 0.36; 95% CI, 0.21 to 0.61) and appeared to overcome differences in prognosis based on the type of driver mutation (<i>JAK2</i> vs. <i>MPL</i> or <i>CALR</i>). In patients with myelofibrosis, clearance of driver mutations at day 30 after transplantation appeared to influence relapse and survival, irrespective of the underlying driver mutation.