AML How do you tell apart myeloblasts from lymphoblasts?
Q. Can you tell me the morphological features of AML M0 and M1 blasts versus ALL blasts to differentiate the two? And are there some hints in the other peripheral WBC cells to tell whether one is dealing with ALL or AML? For example, more lymphocytes possibly pointing to ALL?

A. Those are very good questions. The short answer is that it can be very difficult, and sometimes impossible, to tell the difference between myeloblasts and lymphoblasts without special studies (immunophenotyping or cytochemical stains). However, there are some points that might help:

  1. The myeloblasts in M0 are totally undifferentiated, and therefore impossible to tell apart from other types of blasts (like lymphoblasts). They never have Auer rods, and there are no tiny granules like you sometimes see in myeloblasts in other types of AML. Cytochemical stains (like MPO) won’t work either (that’s how undifferentiated they are!). For these myeloblasts, you really need immunophenotyping to definitively call them myeloblasts.
  2. The myeloblasts in M1 are a bit more differentiated (and the ones in M2 are even more so). There are occasionally Auer rods present, and some of the blasts may have a few fine granules in the cytoplasm. If you see an Auer rod, you know it’s a malignant myeloblast! Check out the blood smear above. It is from a case of AML-M2, and there are three blasts in the photo. The one at the top right has an Auer rod in it. But the other two blasts – if you just saw them alone, you wouldn’t know whether they were myeloblasts or lymphoblasts).
  3. In M0, M1, and M2, you can sometimes see dysplastic changes (hypogranularity and/or hyposegmentation) in the neutrophils that are present, and that can be a useful clue that you’re dealing with an AML as opposed to an ALL (in which the neutrophils look completely normal).
  4. In ALL, we identify and classify the blasts according to their immunophenotype (we don’t use the L1 vs. L2 morphologic classification anymore;). Some clues that you’re dealing with an ALL include a range in size within the blast population (some bigger, more L1-like if you prefer that term, and some smaller with more condensed chromatin, more L2-like). Also, lymphoblasts (and lymphocytes in general) tend to be more fragile than myeloid cells, so you may see some “ghost” or “basket” cells, which are just lymphoblasts or lymphocytes that have been damaged during the smear preparation process. The percentages of the non-blast cells are not useful in making the diagnosis of ALL (i.e., the normal lymphocyte count is not increased in cases of ALL).

The bottom line is: if all you have is a population of plain old undifferentiated blasts (without Auer rods), you really need to do cytochemical stains (and probably immunophenotyping) to tell what lineage they are.

6 Responses to How do you tell apart myeloblasts from lymphoblasts?

  1. Lu Ann Frisch says:

    I have been looking at smears (blood and bone marrow) for 37 years and would NEVER even attempt to differentiate types of blasts by eyeball alone. We have too many excellent tools available to do that more accurately. The patient’s treatment depends on getting it correct! P.S. Love this website !!!!

  2. Kristine says:

    I totally agree!!! On a real patient, there are very very few times when you make a diagnosis without backup of immunophenotyping and/or cytogenetics/molecular studies. With the exception of an AML-M2 with Auer rods, and an APL with faggot cells, you really need to confirm with studies. 37 years! I really respect your experience and opinion. I learned more morphology from the techs in our lab who had been working there for 20+ years than I did from anyone (I’m not sure what your position is – I apologize if you’re a pathologist). Please feel free to chime in and correct me if your experience says otherwise. Thanks for writing in!!

  3. Siti nurmaslina shakirah says:

    the ghost cell=smudge cell??

  4. Kristine says:

    Yes! Ghost cell = smudge cell = basket cell.

  5. balavanthray says:

    What are the differences between myeloblast and lymphoblast?

  6. Kristine says:

    I think you might be asking what each cell types gives rise to (if not, please let me know). Myeloblasts give rise to all granulocytic cells (neutrophils, eosinophils, and basophils) – though we often talk about them in the context of the neutrophil series. Lymphoblasts give rise to lymphocytes (B, T and NK cells).

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