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Despite advances in medicine,
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cancer remains one of the most frightening
diagnoses patients can receive.
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What makes it so difficult to cure
is that it's not one illness,
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but a family of over 100 diseases
occurring in different types of cells.
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And one type of cancer
has the unfortunate distinction
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of afflicting children
more than any other type.
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This is leukemia,
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a cancer that begins in stem cells
found in the bone marrow.
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A stem cell is a bit like an infant,
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undeveloped but possessing
great potential.
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Many stem cells specialize
and become cells of organs,
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like the liver, brain and heart.
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But in some tissues,
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they can continue to divide into new
stem cells throughout development,
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and into adulthood in order to frequently
generate new cells
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and keep up with the body's needs.
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One example is the bone marrow,
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where stem cells differentiate
into many types of blood cells.
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That includes red blood cells,
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which carry oxygen
from the lungs to all tissues,
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platelets, which help stop bleeding
by sticking to damaged blood vessels,
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and white blood cells,
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which patrol the body,
destroying potentially harmful invaders.
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Every once in a while,
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something goes wrong during
a stem cell's specialization process
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and harmful mutations
occur in the cell's DNA.
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Cells with compromised DNA
are supposed to self-destruct,
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but some damaged cells ignore this order,
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replicating uncontrollably,
even as they lose their original function.
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These are what we know as cancer cells.
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It is not yet clear why leukemia
is the most common childhood cancer,
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but one contributing factor may be
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that leukemias are often caused
by just one or two DNA modifications,
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while most cancers require many of them,
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allowing leukemias to arise faster
than other types of cancer.
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Moreover, some DNA alterations
can occur in white blood cells
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during fetal development,
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further increasing the risk
of early leukemia.
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But though it affects more children
than any other cancer,
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adults constitute the majority
of leukemia patients overall.
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Once leukemia strikes, the damaged cells
reproduce in the blood and the bone marrow
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until they take up
all available space and resources.
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When the bone marrow
can no longer produce
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the required amount of functional cells,
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the blood becomes depleted.
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The lack of red blood cells
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means that muscles
don't get enough oxygen,
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the reduced number of platelets
is not sufficient to repair wounds,
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and the dearth of functional white
blood cells impairs the immune system,
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increasing the risk of infections.
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To restore the normal
function of the blood,
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leukemic cells have to be eliminated.
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But because leukemias
are not solid tumors,
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they can't be removed surgically.
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Instead, the cells are killed
inside the body using various treatments
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that include chemotherapy,
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a combination of drugs that destroys
quickly multiplying cells.
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Unfortunately, this has the side effect
of killing healthy cells,
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such as those found in hair follicles
or intestines.
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And in some cases, the dosage
required is so high
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that it kills all cells
in the bone marrow,
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including stem cells.
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When this happens, the body is no longer
able to create new blood cells on its own.
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Fortunately, outside help can come
in the form of stem cells
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from the bone marrow of a donor.
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Once transplanted into the patient,
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they rapidly repopulate
the bone marrow and the blood.
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However, bone marrow transplants
are a complicated process
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requiring antigen compatibility
between the donor and recipient
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to keep the transplanted cells from
from attacking the patient's own cells
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as foreign bodies.
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Unlike with blood transplants,
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there are thousands of HLA types,
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and even siblings and close relatives
may not have compatible bone marrow.
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If this is the case, the search
is expanded to a database
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containing the genetic makeup of millions
of voluntary bone marrow donors.
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The more potential donors there are,
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the more patients lives can be saved
through successful transplants.
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Leukemia may be a frightening disease,
but there is strength and hope in numbers.