Q. I’d like to know how to differentiate between acute leukemia and blast crisis of CML.

A. Great question! To diagnose blast crisis (or blast phase) in chronic myeloid leukemia, you need to have one of the following:

  1. More than 20% blasts in the blood or bone marrow
  2. An extramedullary focus of blasts (e.g., in the skin, lymph nodes, or spleen)
  3. A significant focus of blasts in the bone marrow section

Most of the time, blast crisis presents as a straight-up acute leukemia (more than 20% blasts in the blood or bone marrow). So how would you tell blast crisis apart from a de novo acute leukemia?

Well, you could try to find previous material from the patient – an older bone marrow or blood – and see if there is evidence of CML. Or you could look for the BCR-ABL translocation. This translocation (also called the Philadelphia chromosome) is present in all cases of CML (check it out: ALL cases!) and is only present in a very, very small number of acute leukemias (rare cases of acute lymphoblastic leukemia have the Philadelphia chromosome – if you look closely, though, the breakpoint is different).

But assuming you can’t do those things, the best thing to do is look at the remainder of the cells (the non-blasts). In blast crisis, the remainder of the cells would reflect the underlying CML (a case of which is shown above): you’d see a large percentage of neutrophilic cells (with a left shift) and a basophilia. In a regular old acute leukemia, the remainder of the cells would show a normal differential (more neutrophils than lymphocytes, and a very small number of basophils), and no left shift.

6 Responses to Acute leukemia vs. CML blast crisis

  1. ROFIDA.M.G says:

    Iam medical student ……..good website for medical student

  2. yona rai says:

    will the patient die with crisis blast in acute leukemia?

  3. Kristine says:

    Blast crisis in chronic myleoid leukemia is very difficult to treat. It is even more difficult to treat than an acute leukemia. The mortality in this stage of CML is very high…although some patients do make it through treatment.

  4. Heena Satam says:

    So can we say that a blast phase with >20% myeloblast and left shift (i.e. increased neutrophile count) is considererd as AML case?

    This is because, I would like to know, how clinician would distinguish between A CML and AML condition from blood and BM staining?

  5. Kristine says:

    Good question! Yes – if you have >20% myeloblasts in blood or bone marrow, it is considered AML. The blast count is the key feature in differentiating AML from CML. In CML, the blast count is well below 20% (and you have all the classic features: a high WBC with a left shift, basophilia, a hypercellular marrow, and the Ph chromosome). In AML, the blast count is 20% or more. In some kinds of AML, you count cells other than blasts (like in AML-M3, it’s the promyelocytes that you count).

    Sometimes, in CML, as the disease evolves, the blast count can start going up. If it reaches 20% or more, this is called “blast crisis” – but it is really the same thing (morphologically) as acute leukemia. It’s a lot harder to treat, though, than acute leukemia that arises on its own.

  6. Dr.Kisor Kumar Pal says:

    Very helpful and practical discussion.I learned a lot.

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