CML with Megakaryocytic Blast Crisis: Report of 3 Cases

Chronic myelogenous leukemia (CML) is a chronic myeloproliferative neoplasm consistently associated with the BCR-ABL1 fusion gene located in the Philadelphia chromosome. The Blast Phase is diagnosed when blasts are ≥20% of the peripheral blood white cell count or of bone marrow nucleated cells or when there is an extramedullary blast proliferation. Megakaryocytic blast crisis as the presenting manifestation of CML is extremely rare and only 7 reported cases were found in the literature. Out of 34 cases of CML-Blast Phase between April 2015 and June 2016, 3 cases showed megakaryocytic differentiation. 2 of these presented in Blast phase as the first manifestation of CML and the third case was a known case of CML-Chronic phase. Flow cytometric immunophenotyping was performed on peripheral blood/bone marrow using 6- color flow cytometer Navios. On CD45 vs SSC two distinct populations of blasts were seen in two cases and single population in the third case. All the 3 cases were positive for CD61, cCD41, cCD61 confirming the megakaryocytic lineage. The clinical features, morphologic and cytogenetic findings help in the identification and distinction of megakaryocytic blast phase of CML from Acute Megakayoblastic Leukemia. The diagnosis of such rare presentation of CML is essential for determining the choice of treatment. Therefore including a megakaryocytic marker in the primary flow cytometry panel is important so that these cases are not under-diagnosed as Acute myeloid leukemia because of expression of CD13 and CD33 only.