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Leukemia is a group of cancers of the blood-forming tissues. The word
leukemia tends to be used as an umbrella term. Back in the 19th century it
was one single homogenous disease that was deadly and characterized by a
white appearance of blood samples. However with our growing understanding of
pathologic and cytologic processes we can now differentiate numerous
diseases which require different treatment.
Leukemia, first recognised by the German pathologist Rudolf Virchow in 1847,
starts with tissues such as bone marrow behaving abnormally. This is caused
by a mutation in its DNA. Bone marrow stem cells produce billions of red
blood cells and white blood cells each day, respectively carrying oxygen and
fighting disease around all parts of the body. Leukemia is characterised by
an excessive production of abnormal versions of these cells, overcrowding
the bone marrow. This results in decreased production and function of normal
blood cells. Leukemia can spread to the lymph nodes, spleen, liver, central
nervous system and other organs.
As with all cancers, leukemia is a broad term covering a spectrum of
diseases. In leukemia, the diseases are classified according to the type of
abnormal cell found most in the blood. Leukemia is also clinically split in
to its acute and chronic forms. The four main forms are:
* Acute lymphocytic leukemia (ALL)
* Acute myelogenous leukemia (AML)
* Chronic lymphocytic leukemia (CLL)
* Chronic myelogenous leukemia (CML)
The most common forms in adults are AML and CML, whereas in children ALL is
most widely observed.
Acute leukemias are characterised by the rapid growth of immature blood
cells, which then die early (within one to five months.) This crowding makes
the bone marrow unable to produce healthy blood cells. Acute forms of
leukemia are most common in children and young adults (in fact it is a more
common cause of death for children in the US than any other type of
Chronic leukemias are distinguished by the slower excessive buildup of
mature, but still abnormal, blood cells. Typically taking two to five years
to progress, the cells live too long, meaning too many mostly white blood
cells form in the blood. Chronic leukemia mostly appears in older people.
Whereas acute leukemia must be treated immediately, chronic forms are
sometimes monitored for some time before treatment to ensure maximum
effectiveness of therapy.
(The symptoms listed are not exclusive to, nor necessarily indicative of
leukemia.) Damage to the bone marrow results in a lack of blood platelets,
which are important in the blood clotting process. This means people with
leukemia may become bruised or bleed excessively. Similarly, the blood cell
deficiency leads to shortness of breath and fatigue (blood cells are needed
to carry oxygen efficiently around the body). Bone or joint pain may occur,
possibly because of cancer spreading to these areas. Headaches and vomiting
are indicative of the cancer having dispersed to the central nervous system.
In the case of acute myelogenous leukemia, small rash-like spots on the skin
as well as enlarged gums are typically evident. Acute lymphocytic leukemia
can cause the thymus to become enlarged, and can mean severe coughing or
even suffocation. Chronic myelocytic leukemia can lead to enlargement of the
spleen. Chronic lymphotic leukemia can manifest itself as oversized lymph node.
Scientists are still actively searching for the exact cause of leukemia. The
bone marrow stem cells are thought to become cancerous because of mutation
to their DNA. This could come from exposure to radiation, carcinogenic
substances, or translocation (swapping) of genetic material in the
chromosomes. It is possible to test whether some of these translocations
have occurred in a person's chromosome, confirming whether they have or are
likely to develop leukemia. Similar genetic tests can also determine the
aggressiveness needed in treatment and also the expected prognosis.
Viruses have also been linked, with varying levels of speculation, to some
forms of leukemia. T-cell leukemia has recently been confirmed to be the
result of two viruses.
In the early 1990s concern was raised in the UK about the effect of nuclear
power plants on unborn children, when clusters of leukemia cases were
discovered nearby to some of these plants. The effect was speculative
because clusters were also found where no nuclear plants were present, and
not all plants had clusters around them. Using statistical analysis
researchers at Southampton University concluded that a link was present,
deducing that radiation damage to men working at the plants had caused
genetic abnormalities in their children. After this report British Nuclear
Fuels initially advised workers who were being exposed to high levels of
radiation not to father children, although they have since withdrawn this advice.
Major treatments include chemotherapy and radiation therapy. These are
typically used in combination to maximise effectiveness and reduce any
particular side effect. Because of the severity of some courses, bone marrow
transplants are sometimes necessary. Healthy bone marrow transplanted in to
the body helps rebuild tissue damaged by the treatment.
27,900 adults and 2,300 children are diagnosed each year with leukemia in
the US. Over the last thirty years, the chances of survival have doubled,
although they remain still quite low. These range from a 22 per cent
survival rate in 1970 to 43 per cent rate in the 1990s.