In most cases of leukemia, there are too many abnormal white blood cells. These leukemia cells crowd out the normal blood cells in your bone marrow and build up in your lymph nodes, liver, and spleen. This makes it hard for your body to fight infections.

Your white blood cells help your body fight infection. Your red blood cells make sure all your body parts have the oxygen they need. Your platelets keep you from bleeding too much. When the leukemia cells crowd out your normal cells, your blood cannot do its job. You may bleed or bruise easily, have more infections, and feel very tired.

Chemotherapy or radiation that is used to treat other cancers, such as breast cancer or Hodgkin's lymphoma, can sometimes cause leukemia months or years later.² (This is rare.)

Survival rates are different for different kinds of leukemia. A 5-year survival rate is the percentage of people who are still alive 5 years or more after being diagnosed. But keep in mind that everyone is different. These numbers do not necessarily show what will happen in your case. Researchers are continuing to develop new and better treatments for leukemia. The 5-year survival rates are:

• 20% to 40% for acute myelogenous leukemia (AML) (depending on which type).³
• 74% for chronic lymphocytic leukemia (CLL).³
• Over 70% for people with chronic myelogenous leukemia (CML) who receive a bone marrow transplant. (This applies to people age 50 or younger who are treated in the first year after diagnosis. Transplants are not as successful for older people or for people who have had CML for more than a year.)⁴ Taking imatinib (Gleevec) for a long time might help many people live longer. But long-term studies have not yet been done.⁵

Acute lymphoblastic leukemia (ALL) is different for children than for adults. With treatment, nearly 80% of children and 40% of adults are leukemia-free for a long time afterward.⁶