Background: Thrombocytosis is usually seen in myeloproliferative disorders (MPD) and seldom in acute myeloid leukemias (AML). In acute megakaryoblastic leukemia, platelet counts might exceed 1000×109/L in approximately 30% of patients, while others are frequently presented by cytopenias. To our best knowledge there is no report in the literature on acute mono-megakaryoblastic leukemia, especially with extreme thrombocytosis and complex karyotype abnormalities.
Case Report: We present the case of a 55-year-old woman with acute mono-megakaryoblastic leukemia with extreme thrombocytosis (greater than 2000×109/L) and complex karyotype abnormalities. The patient was first treated with anti-aggregate therapy and later the patient was put on a regimen consisting of idarubicin 10 mg/m2 daily for 3 days and 200 mg Cytosar daily for 7 days. However, a severe pancytopenia occurred at the first day after chemotherapy and the patient died from intracranial hemorrhage.
Conclusions: Extreme thrombocytosis and complex karyotype abnormalities in acute mono-megakaryoblastic leukemia are associated with poor outcome.

Keywords: karyotype abnormalities, Thrombocytosis, acute leukemia