Acute Monocytic Leukemia is cancer of a specific type of the white blood cells. Most blood cells form in the bone marrow. In leukemia, immature blood cells become cancerous. These cells crowd out the healthy blood cells in the bone marrow.

Different types of leukemia depend on the type of blood cell that becomes cancer. Monocytes compose 2% to 10% of all leukocytes in the human body and serve multiple roles in immune function,  including replenishing resident macrophages under normal conditions; migration response to inflammation signals from sites of infection in the tissues; and differentiation into macrophages or dendritic cells to effect an immune response. In an adult human, half of the monocytes are stored in the spleen. Monocytes are generally identified in stained smears by the large kidney shaped or notched nucleus. These change into macrophages after entering into appropriate tissue spaces, and can transform into foam cells in endothelium.  White blood cells are the most common type of blood cell to become cancer. But red blood cells (cells that carry oxygen from the lungs to the rest of the body) and platelets (cells that clot the blood) may also become cancer.

Acute Monocytic Leukemia occurs most often in adults older than 55 years, but it can also develop to a small degree in children under 10.

Leukemia can be either acute or chronic. Acute leukemia is a fast-growing cancer that usually gets worse quickly. Chronic leukemia is a slower-growing cancer that gets worse slowly over time. The treatment and prognosis for leukemia depend on the type of blood cell affected and whether the leukemia is acute or chronic.