Acute megakaryoblastic leukemia is a rare form of AML that occurs primarily in childhood, and especially in children with Down syndrome (DS-AMKL). In this specimen, however, there is transformation of an Essential Thrombocytemia in an adult patient. This progression is also relatively rare. Although ET transforms to an AML in ~5% of cases, these are usually myeloid/neutrophilic or monocytic forms.

Much of the blasts exhibit the bulges ("blebbing") of the cytoplasm and nucleus as is common in the megakaryocyte. Contrary to what you might expect, the platelet count was reduced (90*10^9/L).