proliferation of malignant blast cells. Malignancy of blood-forming tissue, typically the white blood cells. From Greek: “leuk” = white “emia” = blood “Blast”refers to a malignant leukemia cell However, normal bone marrow can have a few normal blasts that are not malignant. Under 5% blasts can be normal Leukemia has by definition > 25% blasts at diagnosis. The diagram below shows the normal deve..