Leukemia

Leukemia is a form of cancer in which the bone marrow makes too many white blood cells. There are over a dozen types of leukemia, but the following four types are the most common:

Acute lymphocytic leukemia (ALL): In ALL, too many stem cells develop into a type of white blood cell called lymphocytes. This type of leukemia usually gets worse quickly if not treated. It often occurs in children.
Acute myeloid leukemia (AML): In AML, the stem cells usually develop into a type of white blood cell called myeloblasts (early granulocytes) which never become mature white blood cells. This type of leukemia usually gets worse quickly if not treated. It may occur in both adults and children.
Chronic lymphocytic leukemia (CLL): In CLL, too many stem cells develop into lymphocytes. This type of leukemia usually gets worse slowly. It often occurs during or after middle age.
Chronic myeloid leukemia (CML): In CML, the stem cells usually develop into myeloblasts (early granulocytes) which never become mature white blood cells. This type of leukemia usually gets worse slowly. It occurs mainly in adults.

Symptoms and Diagnosis

Possible signs for leukemia include:

Fever.
Weakness or feeling tired.
Easy bruising or bleeding.
Petechiae (flat, pinpoint spots under the skin caused by bleeding).
Shortness of breath.
Weight loss or loss of appetite.
Pain in the bones or stomach.
Pain or feeling of fullness below the ribs.
Painless lumps in the neck, underarm, stomach, or groin.

To diagnose leukemia, the following tests and procedures may be used:

Physical exam and history.
Complete blood count (CBC).
Blood chemistry studies: A procedure in which a blood sample is checked to measure the amounts of certain substances released into the blood by organs and tissues in the body. An unusual (higher or lower than normal) amount of a substance can be a sign of disease in the organ or tissue that produces it.
Peripheral blood smear: A procedure in which a sample of blood is checked for the presence of blast cells, number and kinds of white blood cells, the number of platelets, and changes in the shape of blood cells.
Bone marrow aspiration and biopsy: The removal of a small piece of bone and bone marrow by inserting a needle into the hipbone or breastbone. A pathologist views both the bone and bone marrow samples under a microscope to look for signs of cancer.
Cytogenetic analysis: A test in which the cells in a sample of blood or bone marrow are viewed under a microscope to look for certain changes in the chromosomes.
Immunophenotyping: A process used to identify cells, based on the types of antigens or markers on the surface of the cell.

Causes

All cancers are caused by dysfunctions of proteins involved in cell division, apoptosis, or DNA repair (see general characteristics). Dysfunctional proteins may arise from gene mutations or protein interactions with environments. Most leukemia cases are caused by chromosome aberration, resulting in the fusion of two genes, thereby altering normal gene functions (more info). The chromosome aberration may be inherited, or by exposure to environmental factors that damage DNA in the chromosome. Some established risk factors are listed below:

Radiation - nuclear radiation or exposure to x-rays before birth.
Benzene - which is found in tobacco smoke, vehicle emissions, and gasoline fumes.
Chemotherapy - most chemotherapeutic drugs can damage DNA.
Viral Infection - such as human T-cell leukemia/lymphotropic virus type I (HTLV-1) which causes adult T-cell leukemia

Treatment

Acute leukemia (ALL or AML) requires immediate treatment. It usually has two phases.

Remission induction therapy: This is the first phase of treatment. Its purpose is to kill the leukemia cells in the blood and bone marrow. This puts the leukemia into remission.
Maintenance therapy: This is the second phase of treatment. It begins after the leukemia is in remission. The purpose of maintenance therapy is to kill any remaining leukemia cells that may not be active but could begin to regrow and cause a relapse. This phase is also called remission continuation therapy.

For all types of leukemia, the following methods are often used to kill leukemia cells:

In order to giving high doses of chemotherapy or radiation therapy, stem cell transplant may be used.

Other Treatment options include biologic therapy and the following new drugs:

Imatinib (Gleevec) - a tyrosine kinase inhibitor which blocks the enzyme, tyrosine kinase, that causes stem cells to develop into more white blood cells (granulocytes or blasts) than the body needs.
Arsenic trioxide and all-trans retinoic acid (ATRA) - the anticancer drugs that kill leukemia cells, stop the leukemia cells from dividing, or help the leukemia cells mature into white blood cells. These drugs are used in the treatment of a subtype of AML called acute promyelocytic leukemia.

Reference:

National Cancer Institute, USA.