Generally, the nucleus of a blast has a round shape and, depending on the cell line, shape changes of the nucleus occur with maturation. However, bilobular nuclei can occur in Acute Myeloid Leukemia. This abnormality is usually associated with Acute Promyelocyte Leukemia (APL), in which case it is often referred to as "Angel Wings."

The blasts below are all from non-APL acute leukemias.