Leukemia or leukaemia is cancer of bone marrow (tissue in the middle of the bones) and blood causing abnormal accumulation of white blood cells (leukocytes).

In normal, healthy human body white blood cells tend to defend body against infections. Those leukocytes (developed due to leukemia) aren't the same as normal white blood cells and do not function properly. Also those cells block production of normal white blood cells making body unable to fight infections.

Leukemia usually affects younger population and it's the main type of malignant disease among children in US. It can also affect anyone no matter the age, although males are more commonly affected than females.

The main symptoms of leukemia are similar to many other diseases and the only way diagnose can be made is through blood and bone marrow tests. Those symptoms may include:

- fatigue
- weakness
- headache
- fever
- chills
- night sweating
- loss of appetite and weight
- bone and joint pain
- swollen tonsils
- often bruising
- shortness of breath
- long time bleeding from small cuts
- often infections
- liver and spleen enlargement
- skin rash
- pale skin

According to affected blood cell type leukemia can be split into lymphocytic (affects lymphoid cells) and myelogenous (affects myeloid cells). Each type has its acute and chronic form.

Acute leukemia has fast progression ant it's characterized by accumulation of immature blood cells. Due to its rapid progress immediate treatment is required.

Chronic leukemia has slower progression and it's characterized by accumulation of more mature but still abnormal cells.

So generally there are 4 main types of Leukemia:

Acute lymphocytic leukemia (ALL) - the most common type affecting children although it can also affect older people especially in the age of 65 or older.

Chronic lymphocytic leukemia (CLL) - most commonly affects older adults over the age of 55. Younger adults are very rarely affected. It always never occurs in children.
There is specific subtype of CLL named Hairy Cell Leukemia (HCL) which is, unlike any other kind of leukemia, characterized by low white blood cells count.

Acute myelogenous leukemia (AML) - affects adults more commonly then children. It's also known as "acute nonlymphocytic leukemia".

Chronic myelogenous leukemia (CML) - almost always affects adults. Children are very rarely affected.

Causes of leukemia are completely unknown. According to scientific research there are some possible causes that may include genetic predispositions, some kind of viruses, chemicals and radiation. Thus the prevention of leukemia isn't possible yet.

Treatment is different for each type of disease and it always includes chemotherapy.