Case Presentation: A 21-year-old woman was referred to the hematology clinic for further workup for thrombocytosis which was found upon evaluation for vasovagal syncope. The patient was asymptomatic with no pertinent past medical or family history. Upon presentation, the patient was vitally stable and physical examination was normal. Labs were relevant for a white blood cell count of 6.6 x10^3/µL, with 56% neutrophils, 33% lymphocytes, 7% monocytes, and 1% basophils, 0.2% eosinophils, Hemoglobin of 13.4 x10^3/µL, Platelets of 764 K/µL and minimally elevated ESR at 39 mm/hr. The patient was commenced on daily low-dose aspirin. Meanwhile, the thrombocytosis workup for myeloproliferative disorders (MPD) with peripheral blood JAK2 Exon 12,14, CALR (Calreticulin) and MPL genes were unmutated. CT scan of the abdomen and pelvis was performed and was unremarkable.Initial peripheral blood fluorescence in-situ hybridization (FISH) for BCR‐ABL1 was negative. As platelet count continued to rise, the patient had a bone marrow biopsy which revealed a translocation t(9;22) BCR/ABL1 consistent with chronic myeloid leukemia (CML). The patient was then started on a second-generation tyrosine kinase inhibitor Dasatinib. The patient achieved complete cytogenetic and molecular remission and the patient was referred for stem cell transplant evaluation.
Discussion: The annual incidence of CML in the United States is about 4800 cases. CML usually presents with marked leukocytosis, but rarely presents with an isolated, marked thrombocytosis. Thrombocytosis could be reactive or it may be paraneoplastic where it is triggered by an altered immune response to myeloproliferative syndromes including polycythemia vera, CML or as an essential thrombocytosis (ET). With the success of tyrosine kinase inhibitor (TKI) therapy, the all-cause annual mortality rate was reduced to 2% despite the increasing prevalence of CML with time.
Conclusions: BCR/ABL negative or atypical CML is a rare hematologic malignancy. It should be high on the differential diagnosis for cases of significant thrombocytosis, even when it is accompanied by slight leukocytosis. It has a very poor prognosis with a median overall survival of 24 months. These patients should undergo genetic testing for the BCR/ABL gene in order to confirm the diagnosis and tailor therapy.