The allogeneic stem cell transplantation is the only curative treatment for myelofibrosis. However, because of complications such as infection, graft-versus-host disease and conditioning toxicity, this procedure is associated with a high morbidity-mortality rate. The discovery of molecular and genetic markers permitted to improve therapeutic strategy and survival of patient in the last few years. In this study, the investigators want to make an overview of survival, incidence of relapse and incidence of acute and chronic graft versus host disease in allogeneic stem cell transplantation for myelofibrosis, in five centers in France, between 2007 and 2017.