Background: Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm (MPN) with abnormal fusion gene, characterized with an usually distinct initial presentation of neutrophilic leukocytosis and splenomegaly.

Aims: Case report of a CML patient with initial extreme thrombocytosis and treatment approach.

Methods: A 74-year-old man was admitted in the clinic for diagnostic work-up and therapy because of high platelet count. He was asymptomatic, thrombocytosis was incidentally detected.

Results: 0Blood count results were: Hb-93g/l, WBC-17×109/l, Plt-2467×109/l; blood smear displayed Sg-76%, Ly-17%, Mo-4%, Eo-1%, Ba-2%, marked increase in platelets with giant and hypogranulated forms. He had mild hepatomegaly, but no splenomegaly. Bone marrow was hypercellular with myeloid hyperplasia, 2% myeloblasts and increased number of megakaryocytes with clustering and monolobated forms, indicative of MPN/CML. Features were suggestive of essential thrombocytosis, but molecular analysis was negative for typical mutations. Philadelphia chromosome t(9;22)(q34;q11) was detected in all bone-marrow metaphases analyzed, proved with positive BCR/ABL1 FISH analysis result. Subsequently RT-PCR analysis for BCR/ABL1 rearrangement showed the presence of typical b3a2 fusion gene. The patient was diagnosed with CML, chronic phase, associated with extreme thrombocytosis. Considering the high platelets count that is usually associated with high thrombotic risk or bleeding potential due to platelet dysfunction in MPN, complete tests of hemostasis were performed. They showed normal platelet function, 100% aggregation and 0% inhibition with ADP and arachidonic acid, coagulation tests were within reference ranges. Target therapy with nilotinib 2x300mg was started and clopidogel 75mg was added. After one course of nilotinib treatment, the patient’s platelets were reduced to normal levels-358×109/l. He achieved deep molecular response (DMR) at 3 months nilotinib therapy. The patient even experienced mild COVID-19 infection without complications. His DMR remains stable.

Conclusions: Both morphologic and cytogenetic combined with molecular analysis are required for correct MPN-type diagnosis, which is important, as the disease outcome is based on proper initial therapy.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/chronic-myeloid-leukemia-with-extreme-thrombocytosis-as-unusual-initial-presentation/