Pediatric Non-Down Syndrome Acute Megakaryoblastic Leukemia With Unusual Immunophenotype

Acute megakaryoblastic leukemia (AMKL) is a rare subtype of acute myeloid leukemia (AML) characterized by abnormal megakaryoblasts expressing platelet-specific surface antigens. 4%-16% of childhood AMLs are AMKL. Childhood AMKL is usually associated with Down syndrome (DS). It is 500 times more common in patients with DS when compared to the general population. In contrast, non-DS-AMKL is much rarer. We describe a case of de novo non-DS-AMKL in a teenage girl child who presented with a history of excessive tiredness, fever, abdominal pain for three months, and vomiting for four days. She had lost appetite, and weight. On examination she was pale; there was no clubbing, hepatosplenomegaly or lymphadenopathy. There were no dysmorphic features or neurocutaneous markers. Laboratory tests showed bicytopenia (Hb: 6.5g/dL, total WBC count: 700/µL, platelet count: 216,000/ µL, Reticulocyte %: 0.42) and 14% blasts on the peripheral blood smear. Platelet clumps and anisocytosis were also noted. Bone marrow aspirate showed a few hypocellular particles with dilute cell trails but showed 42% blasts. Mature megakaryocytes showed marked dyspoiesis. Flow cytometry on bone marrow aspirate showed myeloblasts and megakaryoblasts. Karyotyping showed 46 XX. Hence, a final diagnosis of non-DS-AMKL was established. She was treated symptomatically. However, she was discharged on request. Interestingly, the expression of erythroid markers such as CD36 and lymphoid markers like CD7 is usually seen in DS-AMKL and not in non-DS-AMKL. AMKL is treated with AML-directed chemotherapies. Although complete remission rates are similar to other AML subtypes, overall survival is only about 18-40 weeks.