Leukemia is cancer of your blood cells. In patients with leukemia, immature blood cells become cancerous, work improperly and begin to crowd out healthy blood cells within the bone marrow.

Leukemia is the most common cancer in children under 15 years, but can also occur in adults older than 55 years. Leukemia can be either acute or chronic—acute leukemia is fast-acting and typically worsens quickly. Chronic leukemia progresses more slowly over time. Treatments and prognosis for patients with leukemia depend on whether the leukemia is acute or chronic, and on the type of blood cell affected by it.

The four main types of leukemia include:

• Acute myeloid leukemia (AML): The most common type of acute leukemia
• Chronic myeloid leukemia (CML): Generally slow-growing, it can sometimes become acute
• Acute lymphocytic leukemia (ALL): Rapids progressing leukemia, most commonly occurring in children under 15 years, and rarely in adults over the age of 45 years
• Chronic lymphocytic leukemia (CLL): Usually slow-growing cancer that begins in the bone marrow before progressing into the bloodstream