Chronic Myeloid Leukemia Presenting with Megakaryocytic Blast Crisis: a Case Report with a Favorable Outcome

Chronic myeloid leukemia (CML) belongs to the chronic myeloproliferative neoplasms, a clonal disorder of pluripotent hematopoietic stem cells, arising because of a hallmark genetic anomaly- reciprocal translocation between chromosomes 9 and 22, known as the Philadelphia chromosome, which generates the BCR::ABL fusion gene. The disease can have a biphasic/triphasic evolution, comprised of an accelerated phase and a terminal blast phase (usually biphasic when blastic phase is lymphoid in nature). Most cases present during the chronic phase of the disease, with only 10% of cases presenting in the blast phase. Megakaryocytic blast crisis is an unusual form of presentation, accounting for less than 3% of cases and it commonly carries an unfavorable prognosis compared to the classic myeloid, lymphoid or even mixed lineage blast crises. Aim: To bring forth an unusual case of CML presenting with megakaryocytic blast crisis and the therapeutic challenges associated with this particular presentation, unexpectedly ending with a favorable outcome. Matherial and methods: we hereby present the case of a 50 year old female patient, diagnosed in 2015 with CML- megakaryocytic blast crisis, who underwent treatment with a tyrosine kinase inhibitor (TKI)- imatinib and intensive chemotherapy regimen 3+7, without satisfactory response. A second induction chemotherapy regimen followed (MEC), alltogether with the same TKI and cytoreductive treatment (hydroxyurea/HU), but still without achieving a complete remission. Thus, the TKI was switched to dasatinib and complete normalisation of blood counts followed (including thrombocytes). However, there was still inadequate molecular and cytogenetic response. Therefore, TKI dosage was increased and after 4 months the patient achieved complete remission, with no detectable BCR::ABL transcript. She spent 9 years on the same TKI until important pleural effusion developed, which required switching to another 2nd generation TKI- bosutinib, based on the patients age, genetic profile and commorbidities. She is still in complete remission without detectable BCR::ABL transcript/Philadelphia chromosome to this day (2024). Results and conclusions: this is the case of a rare presentation of CMLmegakaryocytic blast crisis, who underwent both TKI and intensive chemotherapy induction regimens, marked by a favorable unexpected outcome.