In the non-American part of the English speaking world, this is spelt as "Leukaemia".

Leukaemia occurs when the body accumulates abnormal white blood cells. These cells are usually immature and do not function properly. Eventually, they crowd out the normal blood cells - problems arise with shortages in those blood cell lines. Patients with leukaemia suffer from anaemia, susceptibility to infections and impaired clotting.

Types of leukaemia
- Acute Lymphoblastic Leukaemia / Acute Lymphoblastic Leukemia (ALL)
- Chronic Lymphocytic Leukaemia / Chronic Lymphocytic Leukemia (CLL)
- Acute Myeloid Leukaemia / Acute Myeloid Leukemia (AML)
- Chronic Myeloid Leukaemia / Chronic Myeloid Leukemia (CML)

The difference between these types of leukaemias are that acute leukaemias affect blood cells early in their development and they tend to remain immature, having little or no function. Patients with acute leukaemias are more likely to suffer from infections, bruising and anaemia and usually require more immediate treatment.

In chronic leukaemias, the cells involved are more mature and usually retain more normal function. Symptoms are less marked and progression of the disease is slower than in acute leukaemias.

The difference between myeloid (aka myelocytic or myelogenous) and lymphoid (aka lymphoblastic or lymphocytic) leukaemias is the cell lines they affect. The myeloid cell line is the line that gives rise to platelets, red blood cells, granulocytes and monocytes while the lymphoid line is the cell line that gives rise to lymphocytes.

Most leukaemia patients are adults over 60 years of age. Though leukaemia is rare in children (less than 10% of all leukaemias are found in children) it is the most common form of cancer in children.

Acute lymphocytic leukaemia is the most common form of childhood leukaemia, accounting for 80% of childhood leukaemias. The most common form of adult leukaemia is acute myelod leukaemia.

The incidence of leukaemia is slightly higher in males than females.

Leukemia incidence is highest among Caucasian people and lowest among Chinese, Japanese and Korean people.

Exposure to radiation, certain chemicals and certain viruses have been linked to a higher risk of developing leukaemia.

Leukaemia is diagnosed on clinical suspicion leading to blood tests and a bone marrow biopsy.

It depends on the type of leukaemia but chemotherapy is the mainstay of treatment. Sometimes, a bone marrow transplant may be necessary.

The likely outcome varies greatly depending on the type of leukaemia the patient has.

ALL in children used to be a death sentence only one generation ago but advances in medicine have made cures possible in the majority of cases where treatment is available.