Leukemia is a type of cancer of the blood or bone marrow characterized by an abnormal increase of immature white blood cells called “blasts”.

Leukemia is a broad term covering a spectrum of diseases. In turn, it is part of the even broader group of diseases affecting the blood, bone marrow, and lymphoid system, which are all known as hematological neoplasms.

Leukemia is a treatable disease. Most treatments involve chemotherapy, medical radiation therapy, hormone treatments, or bone marrow transplant.

The rate of cure depends on the type of leukemia as well as the age of the patient. Children are more likely to be permanently cured than adults.

Even when a complete cure is unlikely, most people with chronic leukemia and many people with acute leukemia can be successfully treated for years.

Sometimes, leukemia is the effect of another cancer, known as blastic leukemia, which usually involves the same treatment, although it is usually unsuccessful.

About 90% of all leukemias are diagnosed in adults.

Clinically and pathologically, leukemia is subdivided into a variety of large groups. The first division is between its acute and chronic forms:

Acute leukemia is characterized by a rapid increase in the number of immature blood cells.

Crowding due to such cells makes the bone marrow unable to produce healthy blood cells.

Immediate treatment is required in acute leukemia due to the rapid progression and accumulation of the malignant cells, which then spill over into the bloodstream and spread to other organs of the body.

Acute forms of leukemia are the most common forms of leukemia in children.

Chronic leukemia is characterized by the excessive build-up of relatively mature, but still abnormal, white blood cells.

Typically taking months or years to progress, the cells are produced at a much higher rate than normal, resulting in many abnormal white blood cells.

Whereas acute leukemia must be treated immediately, chronic forms are sometimes monitored for some time before treatment to ensure maximum effectiveness of therapy. Chronic leukemia mostly occurs in older people, but can theoretically occur in any age group.

Additionally, the diseases are subdivided according to which kind of blood cell is affected. This split divides leukemias into lymphoblastic or lymphocytic leukemias and myeloid or myelogenous leukemias.

In lymphoblastic or lymphocytic leukemias, the cancerous change takes place in a type of marrow cell that normally goes on to form lymphocytes, which are infection-fighting immune system cells. Most lymphocytic leukemias involve a specific subtype of lymphocyte, the B cell.

In myeloid or myelogenous leukemias, the cancerous change takes place in a type of marrow cell that normally goes on to form red blood cells, some other types of white cells, and platelets.

Combining these two classifications provides a total of four main categories. Within each of these four main categories, there are typically several subcategories.

Finally, some rarer types are usually considered to be outside of this classification scheme.

Acute lymphoblastic leukemia (ALL) is the most common type of leukemia in young children. This disease also affects adults, especially those age 65 and older. Standard treatments involve chemotherapy and radiotherapy.

The survival rates vary by age: 85% in children and 50% in adults.

Chronic lymphocytic leukemia (CLL) most often affects adults over the age of 55. It sometimes occurs in younger adults, but it almost never affects children.

Two-thirds of the affected people are men. The five-year survival rate is 75%. It is incurable, but there are many effective treatments. One subtype is B-cell prolymphocytic leukemia, a more aggressive disease.

Acute myelogenous leukemia (AML) occurs more commonly in adults than in children, and more commonly in men than women. AML is treated with chemotherapy.

The five-year survival rate is 40%, except for APL (Acute Promyelocytic Leukemia), which is over 90%.[6] Subtypes of AML include acute promyelocytic leukemia, acute myeloblastic leukemia, and acute megakaryoblastic leukemia.

Chronic myelogenous leukemia (CML) occurs mainly in adults; a very small number of children also develop this disease.

One subtype is chronic myelomonocytic leukemia.

There is no single known cause for any of the different types of leukemia. The few known causes, which are not generally factors within the control of the average person, account for relatively few cases.

The cause for most cases of leukemia is unknown. The different leukemias likely have different causes.

Leukemia, like other cancers, results from mutations in the DNA. Certain mutations can trigger leukemia by activating oncogenes or deactivating tumor suppressor genes and thereby disrupting the regulation of cell death, differentiation or division.

These mutations may occur spontaneously or as a result of exposure to radiation or carcinogenic substances.

Among adults, the known causes are natural and artificial ionizing radiation, a few viruses such as human T-lymphotropic virus, and some chemicals, notably benzene and alkylating chemotherapy agents for previous malignancies.

The use of tobacco is associated with a small increase in the risk of developing acute myeloid leukemia in adults.

Some studies have linked exposure to some petrochemicals and hair dyes to the development of some forms of leukemia. Diet has very limited or no effect, although eating more vegetables may confer a small protective benefit.



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