What is acute myeloid leukemia? How is it different from myelodysplastic syndromes?

What is AML and how is it different from MDS?

AML is a more aggressive form of a high-risk MDS. In terms of explaining it, I tend to think of MDS as two different diseases. Patients with a lower-risk MDS have what we call a bone marrow failure state where their main issue is having a low red blood cell count, so anemia, or a low platelet count, thrombocytopenia, or a low white blood cell count, or neutropenia. In those cases, there is a low risk of transformation to acute myeloid leukemia and higher-risk MDS. That's almost like a pre-AML state. It still has the bone marrow failure portion of it where patients have low blood counts, but they also have a higher risk of transformation to AML.

Previously, and what we still think of now, is the cutoff between MDS and AML is 20% involvement of the bone marrow with blast or leukemia cells. Patients who have less than 20% are considered to have MDS, and patients with more than 20% are considered to have leukemia. However, in recent years, we've come to see that line can be blurred. And so sometimes now we consider 10 to 20% blast or bad cells to be leukemia.