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If chronic myeloid leukemia is a chronic leukemia, why does it have immature cells?

Posted May 19 2010 5:31pm

Q. If the chronic leukemias have lots of mature cells, and the acute leukemias have immature cells, then how come chronic myeloid leukemia has lots of immature cells? Seems like it belongs in the acute leukemia category!

A. I think the best way to look at it is to oversimplify it a little, to get at the basics, and then put in a little detail.

The oversimplified version is this: Acute leukemias are composed of immature cells (usually blasts), whereas chronic leukemias are composed of mature cells (mostly the ones you normally see in peripheral blood).

The problem with that definition is that it doesn’t quite cover every chronic and acute leukemia. For example, AML-M2 is an acute leukemia that has at least 20% myeloblasts – but there are also a fair number of maturing neutrophils too (promyelocytes, myelocytes, metamyelocytes, and segmented neutrophils). So that doesn’t quite fit. The important thing in this AML, though, is that it does have at least 20% blasts. So you have to call it AML, even though it doesn’t quite “fit” our nice little definition.

Another example that doesn’t quite fit our neat little definition, as you noted, is CML. In CML, most of the cells are pretty mature (segmented neutrophils, metamyelocytes)…but there are some less mature ones too (myelocytes, promyelocytes). The important thing in CML is that there really aren’t very many blasts around at all; certainly not 20% or more like you’d see in AML. So even though it doesn’t quite fit, we put it into the chronic category (and it certainly acts a lot more like a chronic leukemia than an acute one!).

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