Myelomonocytic Leukemia at 20x Magnification

According to the FAB system, there are eight different types of acute myelogenous leukemia (also called acute myeloid leukemia), identified as M0 through M7. Acute myelomonocytic leukemia, which is designated M4, is one of the most common of the eight types, accounting for about one-fourth of all cases of acute myelogenous leukemia. This form of the disease is distinguished by the involvement of a combination of two kinds of immature cells, myeloblasts (precursors of the myelocytes that mature into granulocytes) and monoblasts (precursors of monocytes). Many individuals with acute myelomonocytic leukemia exhibit a chromosomal aberration (inv(16)). The prognosis of such patients is better than that of acute myelomonocytic leukemia patients without the abnormality.