Chronic Myeloid Leukaemia

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What is Chronic Myeloid Leukaemia?

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Chronic Myeloid Leukemia

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Chronic Myeloid Leukaemia usually arises from the precursors of myeloid cells which would subsequently, in normal circumstances, evolve into normal white cells.

Bone marrow is found inside most of the bones in the body. By adulthood, a large proportion of bone marrow has become relatively inactive. Generally speaking, it is the marrow inside the vertebra, ribs and pelvis, which is responsible for producing the blood cells in adults. In times of crisis or when these areas of bone marrow are damaged, marrow activity may switch on in the other bones.

The bone marrow is a collection of cells inside a connective tissue and fatty stroma. It is necessary to understand the different types of cell found within the bone marrow.

Stem cells are the ultimate origin of the other cells. Stem cells differentiate to form 3 main types of 'progenitor' cells. Each of these cells is then responsible to produce red cells, white cells and megakaryocytes (which produce platelets).

There are a number of proteins, which stimulate production of blood cells. These include erythropoietin, (EPO) granulocyte-macrophage colony stimulating factor (GM-CSF), granulocyte-CSF (G-CSF), Interleukin 3, 5 and 6 (IL-3, IL-5, IL-6). Generally speaking, these proteins interact with receptors on the surface of the primitive bone marrow cells and stimulate them to produce the adult cells.

Who gets Chronic Myeloid Leukaemia?

It is relatively uncommon and occurs in approximately 1 in 100,000 people, rarely affecting those below the age of 20 and usually occurring in the 40-50 year age group, with sex incidence being slightly more common in males.

Geographically, the tumour is found worldwide.

Predisposing Factors

The characteristic feature of CML is the presence of certain genetic translocation in affected stem cells in the bone marrow - the translocation between chromosomes 9 and 22 (9;22)(q34;q11) - the so called Philadelphia chromosome. This translocation is believed to be the cause of the unchecked proliferation of the stem cells, with further chromosomal transformations important for further progression of the disease.

The only real predisposing factor for this type of leukaemia is exposure to high doses of radiation such as that caused by nuclear accidents. Most cases occur with no obvious cause. Cigarette smoking has been shown to accelerate the progression to blast crisis.