What causes leukemia and what are the risk factors?

The underlying cause of ALL has never been established with certainty. People living close to areas of nuclear explosions carry a predisposition to ALL because of the high radiation involved. The group that most needs to be careful about radiation exposure is expectant mothers.

Chemicals such as the benzene found in cigarette smoke, and various chemotherapy drugs used in cancer treatment, are also considered to be associated with the development of ALL.

People infected with the HTLV-1 and EBV viruses face an increased risk of developing ALL. Beyond infectious disease, the risk is also higher in people with conditions such as Down syndrome, Klinefelter syndrome, Fanconi anaemia and neurofibromatosis.

AML arises from mutations and abnormalities in the parts of the DNA that govern the growth and division of stem cells in the bone marrow. The likelihood of developing AML rises with age; the average age at diagnosis is 68. Detected more often in men, AML has risk factors that include exposure to cigarette smoke, myelodysplastic syndrome and Down syndrome.

The definitive underlying cause of CLL has not yet been established. Being over 50, being male, exposure to chemical agents used in warfare, and having other family members who have had the disease are all considered risk factors for developing CLL.

CML arises from genetic mutations, although what triggers those mutations is not yet fully understood. They are abnormalities that develop later in a person's life; the genes associated with the disease are not inherited from a parent.

Humans have 23 pairs of chromosomes in total. In an exchange of segments between chromosomes 22 and 9, chromosome 22 becomes shorter than normal and chromosome 9 becomes longer.

The mutated chromosome 22 is called the Philadelphia chromosome and can be detected in 90% of CML patients. The BCR-ABL gene on the Philadelphia chromosome triggers the uncontrolled multiplication of blood cells and causes CML to develop.