Chronic Lymphocytic Leukaemia

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What is Chronic Lymphocytic Leukaemia?

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Chronic Lymphocytic Leukemia

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Leukaemia is the name for a cancer where there is a malignant proliferation of stem cells within the bone marrow. Leukaemic blast cells suppress the normal formation of blood cells (haematopoiesis) within the bone marrow and this means that there are not enough of the normal red cells, white cells and platelets in the blood (pancytopaenia) of patients with the disease. It is not known how the leukaemic cells prevent normal haematopoiesis, but the resultant pancytopaenia is responsible for the clinical manifestations of the disease.

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 the 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.

Lymphoblasts are normal precursor cells in the bone marrow that differentiate to become mature lymphocytes.

Who gets Chronic Lymphocytic Leukaemia?

Chronic Lymphocytic Leukaemia is the most common form of leukaemia in Western countries with an annual incidence of 3 per 100,000 and occurs primarily as a disease of older patients. The peak age at diagnosis is between 60 and 80 years with sex incidence being a 2:1 male predominance.

Geographically, the tumour is found worldwide, although it is much more common in European countries and the United States than in Asian countries. This difference in incidence is thought to be due to genetic factors.

Predisposing Factors

The causes of chronic lymphocytic leukaemia (CLL) are not known but several associations have been observed. Genetic factors are thought to play an important role, as evidenced by the strong racial variations in incidence that do not change with migration. These tumours occur with higher incidence in the relatives of patients with the disease.

Chronic lymphocytic leukaemia is the only leukaemia not found to be associated with exposure to ionising radiation.

There is some evidence linking the development of chronic lymphocytic leukaemia to exposure to environmental toxins such as carbon tetrachloride (dry cleaning agent), farm herbicides and solvents used in the rubber manufacturing industries.

Progression

The Chronic Lymphocytic Leukaemia tumour spreads by expansion within the marrow space and the marrow of the bones in the body. The tumour cells are released into the blood and also populate other areas containing lymphatic tissue - most notably the lymph nodes, liver and spleen.

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