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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.
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.
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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
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 malignant disease.)
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.
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.
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
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