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Some people with acute myeloid leukemia (AML) have one or more
known risk factors (see "What
are the risk factors for acute myeloid leukemia?"), but most
do not. The cause of their cancer remains unknown at this time. Even
when a person has one or more risk factors, there is no way to tell
whether it actually caused the cancer.
During the past few years, scientists have made great progress
in understanding how certain changes in DNA can cause normal bone
marrow cells to become leukemia cells. Normal human cells grow and
function based mainly on the information contained in each cell's
chromosomes. Chromosomes are long molecules of DNA in each cell. DNA is
the chemical that makes up our genes -- the instructions for how our
cells function. We resemble our parents because they are the source of
our DNA. But our genes affect more than the way we look.
Some genes contain instructions for controlling when our cells
grow and divide. Certain genes that promote cell division are called oncogenes. Others
that slow down cell division or cause cells to die at the right time
are called tumor
suppressor genes.
Each time a cell prepares to divide into 2 new cells, it must
make a new copy of the DNA in its chromosomes. This process is not
perfect, and errors can occur that may affect genes within the DNA.
Cancers can be caused by DNA mutations (changes) that turn on oncogenes
or turn off tumor suppressor genes. For instance, changes in certain
genes such as FLT3, c-KIT, and RAS are commonly found in AML cells.
Mutations in a single gene are found in many cases of AML, but
larger changes in one or more chromosomes are also common. Even though
these changes involve larger pieces of DNA, their effects are still
likely due to changes in just one or a few genes. Several types of
chromosome changes may be found in AML cells:
- Translocations
are the most common type of DNA change that can lead to leukemia. A
translocation means that a part of one chromosome breaks off and
becomes attached to a different chromosome. The point at which the
break occurs can affect nearby genes -- for example, it can turn on
oncogenes or turn off genes that would normally help a cell to mature.
- Deletions
occur when part of a chromosome is lost. This may result in the cell
losing a gene that helped keep its growth in check (a tumor suppressor
gene).
- Inversions
occur when part of a chromosome gets turned around, so it is now in
reverse order. This can result in the loss of a gene (or genes) because
the cell can no longer read its instructions (much like trying to read
a book backwards).
- Addition
means that there is an extra chromosome or part of a chromosome. This
can lead to too many copies of certain genes within the cell. This can
be a problem if one or more of these genes are oncogenes.
Doctors are trying to figure out why these changes occur and
how each of them might lead to leukemia. Not all cases of AML have the
same chromosome changes. Some changes are more common than others, and
some seem to have more of an effect on a person's prognosis (outlook)
than others. For instance, they may affect how quickly the leukemia
cells grow, or how likely they are to respond to treatment. This is
discussed in more detail in the section, "How
is acute myeloid leukemia classified?"
Some people with certain types of cancer have inherited DNA
mutations from a parent. These changes increase their risk for the
disease. But AML is very rarely caused by one of these inherited
mutations.
Most DNA mutations related to AML occur during a person's
lifetime, rather than having been inherited before birth. They may
result from exposure to radiation or cancer-causing chemicals, but in
most cases the reason they occur is not known.
Last Medical Review: 08/06/2009
Last Revised: 08/06/2009
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