CHRONIC MYELOGENEOUS LEUKAEMIA

( By JASCAP )

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What is leukaemia

Leukaemia is a cancer of the white blood cells and can start in bone marrow and lymphatic system.

There are four main types of leukaemia:

  • chronic myeloid Leukemia (CML)
  • acute myeloid Leukemia (AML)
  • chronic lymphocytic Leukemia (CLL)
  • acute lymphoblastic Leukemia (ALL).

Each type of leukemia has its own characteristics and treatment.

What is chronic myeloid leukaemia (CML)?

Chronic myeloid leukaemia (CML) is a rare cancer that causes the body to make too many white blood cells.

About 700 people in the UK are diagnosed with CML each year. It can occur at any age, but is more common in middle-aged and older people and is rare in children.

CML usually develops very slowly. This is why itís described as a Ďchronicí leukaemia. It starts in the bone marrow (where our blood cells are made) in a special type of blood cell called a stem cell. To understand how CML develops, it helps to know a bit about blood and how blood cells are made.

How CML develops?

All cells have a set of instructions that tell them what to do and when to do it. These instructions are stored inside the cells as genes.

Each gene has its own distinct set of instructions that control a particular aspect of how the cell behaves. For example some genes tell a cell when to rest, others tell it when to grow. The genes are organised into structures called chromosomes.

CML develops when, by mistake, a gene gets moved from one chromosome to another one when a stem cell is dividing. The result is a joining together (fusion) of two genes that are normally completely separate. This new abnormal Ďfusioní gene is then passed on to other cells. These are the leukaemia cells.

When doctors look at the leukaemia cells under a microscope, they can see a chromosome that looks different. This chromosome is called the Philadelphia chromosome.

Philadelphia chromosome

Most people with CML (more than 95 out of 100) have the Philadelphia chromosome in all their leukaemia cells. This is known as Philadelphia chromosome positive CML or Ph+CML.

The Philadelphia chromosome isnít inherited so itís not something you were born with and it canít be passed on to your children.

How the Philadelphia chromosome develops?

Most cells in the body contain 23 pairs of chromosomes. They are numbered from 1 to 22, (the 23rd pair are the sex chromosomes XX in women and XY in men).

The Philadelphia chromosome is made when the Abl gene on chromosome 9 is mistakenly transferred to chromosome 22 and attaches to the Bcr gene. This creates a new fusion gene called Bcr-Abl.


Development of the Philadelphia chromosome

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The Bcr-Abl gene makes a protein called tyrosine kinase. Too much tyrosine kinase makes cells behave abnormally and causes the changes in the blood and bone marrow that are found in CML. Newer treatments for CML work by blocking the effects of tyrosine kinase.

Risk factors and causes of CML

The causes of chronic myeloid leukaemia (CML) arenít fully understood, but the ongoing research may shed more light on this issue.

CML, like other cancers, isnít infectious and canít be passed on to other people. It isnít caused by an inherited faulty gene so other members of your family canít develop CML just because you have it.

There are very few known risk factors that might increase a personís risk of developing CML. And for most people with CML, it isnít clear why it developed.

The main factor that is known to increase the risk of developing CML is radiation. Exposure to very high radiation levels (such as accidental exposure following a nuclear accident like the 1986 Chernobyl incident or the explosions in Nuclear plants in Japan due to earth quake followed by the Tsunami of March 2011) is known to increase the risk of developing CML. But very few people in the UK are exposed to radiation levels high enough to increase their risk of developing CML. For most people with CML there is no obvious link to radiation exposure.

In recent years there has been publicity about an increase in leukaemia in people living close to nuclear power plants. Research is still underway to see if there is any definite link between these factors, but as yet there is no evidence of this.

Research also hasnít found any links between exposure to electromagnetic fields, living near high-voltage electricity cables, or household radon and the risk of adults developing CML.

How common is Myeloid leukemia in India?

Leukemia is one of the common types of cancer in India. The incidence (newly diagnosed cases of Cancer in a year) of all types of leukemias together (Acute and Chronic; Lymphoid, Pro-myelocytic and Myeloid) is about 4 persons per 1,00,000 population1.

In India, between the years 2001-2003, across five urban centers - Mumbai, Delhi, Chennai, Bhopal and Bangalore, Ė and one rural center - Barshi, a total of 1,173 cases of Myeloid leukemia (both Acute and Chronic combined) were registered (2.66% of all cancers) for males across all age groups; while 766 cases of Myeloid leukemia (both Acute and Chronic combined) were registered (1.72% of all cancers) for females across all age groups. Considering all men, women and children with all types of cancers together, a grand total of 1,939 cases of Myeloid leukemia (both Acute and Chronic combined) (2.19% of all cancers) were registered at the six centers mentioned above, between the year 2001-20032.

The TATA Memorial Hospital (T.M.H.) in Mumbai, India registered a grand-total of 19,127 cases of all types of cancer patients in the year 2006, for men, women and children combined, out of which 663 (3.5% of the total cases) were diagnosed with the Myeloid leukemia (both Acute and Chronic combined). Out of the total 663 patients diagnosed with Myeloid leukemia (both Acute and Chronic combined), mentioned above at the T.M.H., 450 (68%) were males and 213 (32%) were females3.

Twenty seven percent of all Haematopoetic cancers among men, women and children in the year 2006 at the T.M.H. were attributable to Myeloid leukemia (both Acute and Chronic combined).

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