Myeloid neoplasm with isolated del(5q) and the MPLW515L mutation fulfills the WHO diagnostic criteria for ET.

A 70-year-old male was referred to our hospital for marked thrombocytosis without anemia. The patient simultaneously presented with an MPL W515L mutation, one of the major driver mutations in essential thrombocythemia (ET), and deletion of 5q, a characteristic cytogenetic abnormality in myelodysplastic syndrome (MDS). Bone marrow examination showed a combination of both mature hyperlobulated megakaryocytes, as found in ET, and small hypolobulated megakaryocytes, typically found in MDS with del(5q). The present case is consistent with the recently proposed category of myeloid neoplasms with isolated del(5q) and an MPN driver mutation.