FLT3 and myeloproliferative disorder: One FLT3-ITD mutation was identified in the JAK2V617F-negative group (1.1%), and none were identified in the JAK2V617F-positive group, confirming the absence of FLT3 mutations in JAK2V617F-positive specimens [28], which is basically the same as our results that FLT3 mutation was rare in the usual types of MPN and the two mutations are mutually exclusive.