Chronic Myelogenous Leukemia (CML) Workup

Updated: Jun 23, 2017
  • Author: Emmanuel C Besa, MD; Chief Editor: Koyamangalath Krishnan, MD, FRCP, FACP  more...
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Workup

Approach Considerations

The workup for chronic myelogenous leukemia (CML) consists of a complete blood count with differential, peripheral blood smear, and bone marrow analysis. Although typical hepatomegaly and splenomegaly may be imaged by using a liver/spleen scan, these abnormalities are often so obvious clinically that radiologic imaging is not necessary.

The diagnosis of CML is based on the histopathologic findings in the peripheral blood and the Philadelphia (Ph1) chromosome in bone marrow cells.

Other laboratory abnormalities include hyperuricemia, which is a reflection of high bone marrow cellular turnover, and markedly elevated serum vitamin B-12–binding protein (TC-I). The latter is synthesized by the granulocytes and reflects the degree of leukocytosis.

For more information, see the Medscape Reference article Chronic Myelogenous Leukemia Staging.

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Blood Count and Peripheral Smear

In CML, the increase in mature granulocytes and normal lymphocyte counts (low percentage due to dilution in the differential count) results in a total WBC count of 20,000-60,000 cells/μL. A mild increase in basophils and eosinophils is present and becomes more prominent during the transition to acute leukemia.

These mature neutrophils, or granulocytes, have decreased apoptosis (programmed cell death), resulting in accumulation of long-lived cells with low or absent enzymes, such as alkaline phosphatase (ALP). Consequently, the leukocyte alkaline phosphatase stains very low to absent in most cells, resulting in a low score.

The peripheral blood smear in patients with CML shows a typical leukoerythroblastic blood picture, with circulating immature cells from the bone marrow (see the image below).

Blood film at 400X magnification demonstrates leuk Blood film at 400X magnification demonstrates leukocytosis with the presence of precursor cells of the myeloid lineage. In addition, basophilia, eosinophilia, and thrombocytosis can be seen. Courtesy of U. Woermann, MD, Division of Instructional Media, Institute for Medical Education, University of Bern, Switzerland.

The transitional or accelerated phase of CML is characterized by poor control of blood counts with myelosuppressive medication, the appearance of peripheral blast cells (≥15%), promyelocytes (≥30%), basophils (≥20%), and reduction in platelet counts to less than 100,000 cells/μL unrelated to therapy. Promyelocytes and basophils are shown in the images below.

Blood film at 1000X magnification shows a promyelo Blood film at 1000X magnification shows a promyelocyte, an eosinophil, and 3 basophils. Courtesy of U. Woermann, MD, Division of Instructional Media, Institute for Medical Education, University of Bern, Switzerland.
Blood film at 1000X magnification demonstrates the Blood film at 1000X magnification demonstrates the whole granulocytic lineage, including an eosinophil and a basophil. Courtesy of U. Woermann, MD, Division of Instructional Media, Institute for Medical Education, University of Bern, Switzerland.

Signs of transformation or accelerated phase in patients with CML are poor control of blood counts with myelosuppression or interferon, increasing blast cells in peripheral blood with basophilia and thrombocytopenia not related to therapy, new cytogenetic abnormalities, and increasing splenomegaly and myelofibrosis.

In approximately two thirds of cases, the blasts are myeloid. However, in the remaining one third of patients, the blasts exhibit a lymphoid phenotype, further evidence of the stem cell nature of the original disease. Additional chromosomal abnormalities are usually found at the time of blast crisis, including additional Ph1 chromosomes or other translocations.

Early myeloid cells such as myeloblasts, myelocytes, metamyelocytes, and nucleated red blood cells are commonly present in the blood smear, mimicking the findings in the bone marrow. The presence of the different midstage progenitor cells differentiates CML from the acute myelogenous leukemias, in which a leukemic gap (maturation arrest) or hiatus exists that shows absence of these cells.

A mild to moderate anemia is very common at diagnosis and is usually normochromic and normocytic. The platelet counts at diagnosis can be low, normal, or even increased in some patients (>1 million in some).

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Bone Marrow Analysis

The bone marrow is characteristically hypercellular, with expansion of the myeloid cell line (eg, neutrophils, eosinophils, basophils) and its progenitor cells. Megakaryocytes (see the image below) are prominent and may be increased. Mild fibrosis is often seen in the reticulin stain.

Bone marrow film at 400X magnification demonstrate Bone marrow film at 400X magnification demonstrates clear dominance of granulopoiesis. The number of eosinophils and megakaryocytes is increased. Courtesy of U. Woermann, MD, Division of Instructional Media, Institute for Medical Education, University of Bern, Switzerland.

Cytogenetic studies of the bone marrow cells, and even peripheral blood, should reveal the typical Ph1 chromosome, which is a reciprocal translocation of chromosomal material between chromosomes 9 and 22 (see the image below). This is the hallmark of CML, found in almost all patients with the disease and present throughout the entire clinical course of CML.

The Philadelphia chromosome, which is a diagnostic The Philadelphia chromosome, which is a diagnostic karyotypic abnormality for chronic myelogenous leukemia, is shown in this picture of the banded chromosomes 9 and 22. Shown is the result of the reciprocal translocation of 22q to the lower arm of 9 and 9q (c-abl to a specific breakpoint cluster region [bcr] of chromosome 22 indicated by the arrows). Courtesy of Peter C. Nowell, MD, Department of Pathology and Clinical Laboratory of the University of Pennsylvania School of Medicine.

In addition, the chimeric BCR/ABL messenger RNA (mRNA) that characterizes CML can be detected by polymerase chain reaction (PCR). This is a sensitive test that requires just a few cells and is useful in monitoring minimal residual disease (MRD) to determine the effectiveness of therapy. BCR-ABL mRNA transcripts can also be measured in peripheral blood

Karyotypic analysis of bone marrow cells requires the presence of a dividing cell without loss of viability because the material requires that the cells go into mitosis to obtain individual chromosomes for identification after banding. This is a slow, labor-intensive process.

The new technique of fluorescence in situ hybridization (FISH) uses labeled probes that are hybridized to either metaphase chromosomes or interphase nuclei, and the hybridized probe is detected with fluorochromes. This technique is a rapid and sensitive means of detecting recurring numerical and structural abnormalities. (See the image below.)

Fluorescence in situ hybridization using unique-se Fluorescence in situ hybridization using unique-sequence, double-fusion DNA probes for bcr (22q11.2) in red and c-abl (9q34) gene regions in green. The abnormal bcr/abl fusion present in Philadelphia chromosome–positive cells is in yellow (right panel) compared with a control (left panel). Courtesy of Emmanuel C. Besa, MD.

Two forms of the BCR/ABL mutation have been identified. These vary according to the location of their joining regions on bcr 3' domain. Approximately 70% of patients who have the 5' DNA breakpoint have a b2a2 RNA message, and 30% of patients have a 3' DNA breakpoint and a b3a2 RNA message. The latter is associated with a shorter chronic phase, shorter survival, and thrombocytosis.

CML should be differentiated from Ph1-negative diseases with negative PCR results for BCR/ABL mRNA. These diseases include other myeloproliferative disorders and chronic myelomonocytic leukemia, which is now classified with the myelodysplastic syndromes.

Additional chromosomal abnormalities, such as an additional or double Ph1-positive chromosome or trisomy 8, 9, 19, or 21; isochromosome 17; or deletion of the Y chromosome, have been described as the patient enters a transitional form or accelerated phase of the blast crisis as the Ph chromosome persists.

Patients with conditions other than CML, such as newly diagnosed acute lymphocytic leukemia (ALL) or nonlymphocytic leukemia, may also be positive for the Ph1 chromosome. Some consider this the blastic phase of CML without a chronic phase. The chromosome is rarely found in patients with other myeloproliferative disorders, such as polycythemia vera or essential thrombocythemia, but these cases are probably misdiagnosed CML. It is rarely observed in myelodysplastic syndrome.

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