Chronic Myelogenous Leukemia (CML)

Conditions & Diseases: Cancers

Chronic myelogenous leukemia, also called chronic granulocytic, chronic myelocytic or chronic myeloid leukemia, is a slow, progressive bone marrow and blood type cancer caused by an increased number of granulocytes (a type of white blood cells).

Normally, the body produces three types of blood cells called mature blood cells.

Red blood cells, which carry the oxygen to all the body tissues.
White blood cells, which fight against infections.
Platelets, which control the bleeding by forming blood clots.

Mature blood cells develop from immature bone marrow cells called stem cells. When chronic myelogenous leukemia occurs, too many bone marrow stem cells develop into granulocytes. This phenomenon is caused by a genetic mutation in the chromosome 9 and 22 (called Philadelphia or Ph chromosome).

Recent studies suggest that the end portion of both chromosomes detach from the chromosome’s body and switch places. The detached fragment of the chromosome 9 attaches to the broken end of the chromosome 22, while the detached fragment of the chromosome 22 attaches to the broken end of the chromosome 9 (phenomenon called translocation).

This chromosome translocation occurs only in the stem cells and the blood cells developed from the stem cells. When the end portion of the chromosomes dettach, two genes are disrupted, the ABL (from Abelson) gene of the chromosome 9 and the BCR (for breakpoint cluster region) gene of chromosome 22.During translocation, parts of the ABL and BCR gene combine creating an abnormal fused gene called BCR-ABL. Each gene produces a protein with a certain role. The new protein produced by the BCR-ABL gene functions abnormally causing a dysfunctional growth and survival rate for the cell.

However, this genetic mutation is not present at birth, is not inherited, and it can develop at any time during the life span. Medical researchers have not been able to identify the exact causes of the chromosome translocation, but the evidence from clinical trials and medical experience built up over time reveals strong connections between several risk factors and chronic myelogenous leukemia. The risk factors include:

Exposure to high level radiation like atomic bomb explosions or nuclear power plant accidents.
Medical treatments like high doses of radiation therapy for other types of cancer especially lymphoma.
Diagnosis procedures like dental or medical x-rays.

Chronic myelogenous leukemia usually occurs during or after middle age, being more common among adults. It rarely occurs in children. Chronic myelogenous leukemia progresses slowly and can be asymptomatic in its early stages. In most cases, this type of leukemia is discovered during a routine medical check-up. Some of the most common symptoms are:

Loss of the general well-being.
Feeling tired.
Breathing difficulties during physical activities.
Anemia
Discomfort or swelling in the abdomen cavity caused by an enlarged spleen.
Excessive sweating and low tolerance to warm temperature.
Fever
Unexplained weight loss.
Discomfort below the ribs (pain or fullness sensations).

The number of granulocytes (blasts) and the severity of the symptoms classifies the leukemia in 4 stages. These are:

1. Chronic stage: In this stage, less then 10 percent of the blood and bone marrow cells are blasts, and the patient displays relatively mild symptoms. Patients during this stage respond well to standard treatment.

2. Accelerated stage: In this stage, between 10 and 30 percent of the blood and bone marrow cells are blast cells, and the patient displays several symptoms like fever, poor appetite, and weight loss. Patients during this stage do not respond as well to the treatment as in the chronic stage.

3. Blastic stage: In this stage, more than 30 percent of the blood and bone marrow cells are blast cells, and the blast cells often spread to the bones and tissues adjacent to the bone marrow.

4. Relapse: This stage occurs after the remission (leukemia relapses), and is characterized by an increased number of blast cells.

Article by Alina Morrow, MS
Medical Writer
OmniMedicalSearch.com