These are clinically called ‘Leukaemias'. In fact, these are cancer of the bone marrow which produces the cells, viz. red and white blood cells and the platelets that circulate in the blood. In this condition, the white blood cells produced in the bone marrow are cancerous and immature. They are also produced in number much more than the normal cells. That is why the condition is called leukemia, literally meaning white blood. The other cells produced in the marrow such as the red blood cells and the platelets are produced less.

Untreated, the leukemia are progressive and fatal; death occurs from anaemia, bleeding (haemorrhage) or repeated infections. The course may vary from a few weeks to several years depending upon the severity of the condition and the type of white blood cells involved. Some leukaemias run an acute course, others a chronic one. The leukaemic process affects either the precursors of the lymphocytes, or the granulocytes also called myeloid cells.

Of all the varieties of leukemia, acute lymphoblastic leukemia (ALL) involving the precursors of lymphocyte, i.e. the lymphoblasts, is the commonest in children; it forms one­ third of all childhood cancers. It occurs between the age of 2 to 7 years, and is uncommon after the age of 15 years.

In adults, the common acute leukemia is non­lymphocytic (ANLL), also called acute myelogenous leukaemia (AML) because it involves myeloid cells.

Acute lymphoblastic leukaemia, the type commonly found in children, is rare in adults.

Leukaemias are thus classified as:

Acute lymphoblastic and acute non-lymphoblastic (also called acute myeloid).

Chronic lymphocytic and non-lymphocytic.

Causes of Leukaemias

In the majority of cases the cause of leukemia is unknown. Several factors, however, are known to be associated with the development of leukemia. These are:

1. Ionising Radiation: There was an undoubted increase in leukemia incidence following the atomic bombing of the Japanese cities. A striking increase in leukemia was also observed after the use of X -ray therapy to control an arthritic condition of the spine called ankylosing spondylitis.

2. Cytotoxic Drugs: These, particularly alkylating agents used in the treatment of cancer may induce leukemia after a latent period of several years.

3. Exposure to Benzene: This is a chemical compound used in industries.

4. Retrovirus: It has been found to be associated with one type of leukemia.