Leukemias are a group of diseases characterized by an abnormal proliferation of white blood cells. Acute and chronic leukemias are differentiated by the maturity level of the cells they affect. Acute forms affect immature cells, hindering them from completing their development, and chronic forms involve atypical mature cells.

Leukemias are generally further differentiated by the type of white blood cells they are connected with. Myelogenous leukemias are diseases involving granulocytes and monocytes. Acute myelomonocytic leukemia is a distinct type of myelogenous leukemia as established by the French American British (FAB) classification system.

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.

Many of the early symptoms of acute myelomonocytic leukemia and other types of acute myelogenous leukemia are nonspecific, often consisting of fever, weakness, unexplained weight loss, fatigue, and aching bones and joints. Other indications of disease may include repeated infections, slow wound healing, frequent and easily produced bruising and bleeding, and spotting of the skin. A bone marrow biopsy is usually taken when such signs develop, and is central in diagnosis, but a number of other tests may also be performed, including a spinal tap, which can reveal whether or not the disease has spread to the central nervous system. Involvement of the brain has been known to produce seizures in some patients.

More than 10,000 cases of acute myelogenous leukemia are diagnosed annually. Men are more commonly affected than women and incidence increases with age, though the disease can affect the young and middle-aged as well as the elderly. Certain conditions, most notably Down syndrome, greatly increase the likelihood that an individual will develop acute myelogenous leukemia. Primary treatment for the disease generally consists of chemotherapy, though radiation therapy and bone marrow transplants may also be utilized.

Myelomonocytic Leukemia at 20x Magnification - Overall the cure rate for myelomonocytic leukemia patients less than 60 years of age is about 30 percent, although certain subsets of individuals tend to fare much better or worse. For example, children with acute monocytic leukemia with the inv(16) aberration have a five-year survival rate greater than 60 percent.