White blood cells develop from stem cells in the bone marrow. Sometimes the development goes awry, and pieces of chromosomes get rearranged. The resulting abnormal chromosomes interfere with normal control of cell division, so that affected cells multiply uncontrollably or are resistant to normal cell death, resulting in leukemia.
Classification of leukemia
Leukemias are grouped into four main types:
The types are defined according to how quickly they progress and the type and characteristics of the white blood cells White Blood Cells The main components of blood include Plasma Red blood cells White blood cells Platelets read more 
that become cancerous.
Acute leukemias progress rapidly and consist of immature cells.
Chronic leukemias progress slowly and consist of more mature cells.
Lymphocytic leukemias develop from cancerous changes in lymphocytes or in cells that normally produce lymphocytes. They may be acute or chronic.
Myeloid (myelocytic, or myelogenous) leukemias develop from cancerous changes in cells that normally produce neutrophils, basophils, eosinophils, and monocytes. They may be acute or chronic.
Complications of leukemia
Leukemia cells ultimately occupy the bone marrow, replacing or suppressing the function of cells that develop into normal blood cells. This interference with normal bone marrow cell function can lead to inadequate numbers of:
Normal white blood cells (increasing the risk of infection)
Also, the cancerous white blood cells do not function like normal white blood cells so they cannot help the body fight off infections.
Leukemia cells may also invade other organs, including the liver, spleen, lymph nodes, testes, and brain.
Causes of Leukemia
The cause of most types of leukemia is not known. Exposure to radiation, to some types of chemotherapy, or to certain chemicals (such as benzene, some pesticides, and chemicals in tobacco smoke) increases the risk of developing some types of leukemia, although leukemia develops only in a very small number of exposed people. Certain hereditary disorders, such as Down syndrome Down Syndrome (Trisomy 21) Down syndrome is a chromosome disorder caused by an extra chromosome 21 that results in intellectual disability and physical abnormalities. Down syndrome is caused by an extra chromosome 21... read more 
and Fanconi anemia, increase the risk as well. In some people, leukemia is caused by certain abnormalities of the chromosomes.
A virus known as human T lymphotropic virus 1 (HTLV-1), which is similar to the virus (HIV-1) that causes AIDS, is strongly suspected of causing a rare type of lymphocytic leukemia called adult T-cell leukemia. Infection with the Epstein-Barr virus Infectious Mononucleosis Epstein-Barr virus causes a number of diseases, including infectious mononucleosis. The virus is spread through kissing. Symptoms vary, but the most common are extreme fatigue, fever, sore throat... read more 
(which also causes mononucleosis) has been associated with a rare form of lymphocytic leukemia that occurs in Asia and Africa.
Treatment of Leukemia
Drugs, usually chemotherapy, immunotherapy, and/or targeted therapy
Sometimes stem cell transplantation, radiation therapy, or surgery
Many leukemias can be effectively treated, and some can be cured. Treatment can consist of different types of drugs called
Chemotherapy Chemotherapy and Other Systemic Cancer Treatments Systemic treatments are those that have effects throughout the body rather than being applied directly to the cancer. Chemotherapy is a form of systemic treatment that uses drugs to kill cancer... read more : Chemotherapy consists of drugs that kill dividing cells. Chemotherapy therefore attacks cancer cells because they divide rapidly, but it also can harm normal cells.
Immunotherapy Immunotherapy for Cancer Immunotherapy is used to stimulate the body's immune system against cancer. These treatments target specific genetic characteristics of the tumor cells. The genetic characteristics of tumors... read more : Immunotherapy is a cancer treatment that uses a person's own immune system to kill cancer cells.
Targeted therapy: Targeted therapy consists of drugs that attack a cancer cell's innate biologic mechanisms.
Both immunotherapy and targeted therapy are less likely to kill normal cells than chemotherapy does and are, therefore, better tolerated. Doctors select the particular drug or combination of drugs based on the classification of the leukemia. Sometimes, stem cell transplantation Stem Cell Transplantation Stem cell transplantation is the removal of stem cells (undifferentiated cells) from a healthy person and their injection into someone who has a serious blood disorder. (See also Overview of... read more , radiation therapy Radiation Therapy for Cancer Radiation is a form of intense energy generated by a radioactive substance, such as cobalt, or by specialized equipment, such as an atomic particle (linear) accelerator. Radiation preferentially... read more , or surgery is used.
The complications of leukemia may require treatment. People may need blood transfusions if leukemia has caused severe anemia. They may need antibiotics if infections develop. If bleeding occurs, they may need platelet transfusions.
When leukemia is under control, the number of abnormal cells in the bone marrow is very low, and people are said to be in remission. If numbers of leukemia cells increase again, people are said to have a relapse.
For some people in relapse, quality of life eventually deteriorates, and the potential benefit for further treatment may be extremely limited. Keeping people comfortable may become more important than trying to modestly prolong life. Affected people and their family members must be involved in these decisions. Much can be done to provide compassionate care Treatment Options at the End of Life Often, the available choices for end-of-life care involve a decision whether to accept the likelihood of dying sooner but to be more comfortable or attempt to live slightly longer by receiving... read more , relieve symptoms, and maintain dignity.
More Information
The following is an English-language resource that may be useful. Please note that the MANUAL is not responsible for the content of this resource.
Leukemia & Lymphoma Society: Provides disease information for people with leukemia and their caregivers and resources for support
