Atypical myeloproliferative disorders in adults.

The definition of 'atypical MPDs' includes all chronic myeloid disorders that defy classification as either MDS or classic MPDs. These can be both molecularly defined or clinicopathologically assigned: chronic myelomonocytic leukemia, juvenile myelomonocytic leukemia, chronic neutrophilic leukemia, chronic basophilic leukemia, chronic eosinophilic leukemia, idiopathic eosinophilia including hypereosinophilic syndrome, systemic mastocytosis, unclassified MPD, and eosinophilic/mast cell disorders associated with mutations of PDGFR, FGFR1, and KIT all fall under the category of atypical MPDs.