AML (acute myeloid leukemia) is a cancer of the white blood cells. It is defined as having more than 20 out of 100 cells in your bone marrow being young white blood cells (blasts). About 30 out of 100 people with MDS will develop AML. Certain subtypes of MDS are more likely to become AML. If you have RAEB-1 or RAEB-2 subtype of MDS, you have a greater than 4 in 10 chance of developing AML. Both aplastic anemia and PNH patients have a small chance of developing AML later in their disease.