Previous studies have reported FLT3 mutation in as many as 9.2% of myeloproliferative neoplasms (MPNs) and myelodysplastic/myeloproliferative neoplasms (MDS/MPNs), as well as in chronic myelogenous leukemia, that are negative for the JAK2V617F gene mutation; no FLT3 mutation has been found in JAK2-positive MPNs, suggesting that the mutations are mutually exclusive.
Refractory anemia with ring sideroblasts (RARS-T) associated with marked thrombocytosis is a myelodysplastic/myeloproliferative neoplasm associated with both SF3B1 and JAK2 or MPL mutations.
Atypical CML should therefore be considered as a JAK2 negative chronic myeloid neoplasm that remains properly categorized, alongside chronic myelomonocytic leukemia and juvenile myelomonocytic leukemia, within the WHO group of myelodysplastic/myeloproliferative neoplasms.