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A 7 8-year-old female patien t presen ts with fatigue and weakness . On physical exam. she has splenomegaly. CBC shows leukocyte count of 1 5 , LJOO/pl with 38% monocytes and 22% eosinophi ls; hemoglobin is 1 0.3 g/d l and platelet count is 1 LJ3.000/pl. The blood smear is depicted below.
Based on the clinical presentation and above laboratory results, a diagnosis of chronic myelo-monocytic leukemia ( CMML) is considered. Which of the following tests is most important in the diagnostic evaluation of this disease?
- Evaluation for BCR-ABL fusion gene
- FISH for trisomy 8
- FISH for isochromosome 17 q
- JAK2 mutation
Medicine
A. The peripheral blood smear shows monocytosis and increased eosinophils, and a few eosinophils demonstrate hyposegmented nuclei and hypogranulation. Basophilia and a myeloid left shift are not evident. Nonetheless, a positive test for the presence of the Philadelphia chromosome gene fusion product BCR-ABL would be consistent with chronic myeloid leukemia, rather than CMML, and thus a negative finding for this gene is part of the diagnostic criteria of CMML. In addition, a posi-tive test would diagnose chronic myelogenous leukemia, and the treatment would be different from that of CMML. Trisomy 8 and isochromosome 17 q are genetic aberrations associated with a hemato-logic disorder referred to as "atypical CML:' JAK2 mutation is positive in patients with myeloprolifera-tive neoplasms, but only in a small minority of patients with CMML.
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