A Case of Chronic Myelogenous Leukemia Occurring in a Patient Treated for Essential Thrombocythemia

BACKGROUND Essential thrombocythemia (ET) is one of the BCR-ABL gene fusion negative chronic myeloproliferative disorders (MPDs), which also include polycythemia vera (PV), and myelofibrosis. Few clinical cases have reported the progression of ET to chronic myelogenous leukemia (CML) with the expression of the BCR-ABL gene. This report describes such a case and includes a review of other reported cases of CML co-occurring with BCR-ABL-negative chronic MPDs. CASE REPORT A 49-year-old woman was diagnosed with ET in 2007. Cytogenetic testing was negative for expression of the JAK2 or BCR-ABL1 genes. Eight years later, in January 2015, she presented with excessive fatigue, poor appetite, unintentional weight loss, a white blood cell (WBC) count of 24,700 per mL, hemoglobin of 9.9 g/dl, and a platelet count of 557,000 per mL, with blasts and basophils in the blood film. Cytogenetic analysis with fluorescent in situ hybridization (FISH) confirmed a 9: 22 chromosomal translocation (Philadelphia chromosome), and quantitative reverse transcription polymerase chain reaction (qRT-PCR) detected the expression of the BCR-ABL gene, confirming a diagnosis of CML. In February 2015, first-line therapy commenced with nilotinib, which was changed to imatinib after three months. During the following nine months, qRT-PCR confirmed a trend to deep molecular remission (MR5). However, she developed early myelofibrosis, and myelosuppressive therapy was resumed. CONCLUSIONS This rare case highlights the importance of cytogenetic testing in cases of CMPD that transform to CML, not only to confirm the diagnosis but to plan treatment, as Philadelphia chromosome-positive and -negative cases differ in their management.