The exact cause of most bone cancers is not known.
However, scientists have found that bone cancers are associated
with a number of other conditions, which are described in the section
on risk factors. Keep in mind that most people with bone cancers
do not have any known risk factors and that the causes of their
cancers remain unknown at this time. Research is underway to learn
more about these causes.
During the past few years, scientists have made great progress in
understanding how certain changes in a person's DNA can cause bone
cells to become cancerous. DNA carries the instructions for nearly
everything our cells do. We usually look like our parents because
they are the source of our DNA. However, DNA affects more than our
outward appearance. It may influence our risks for developing certain
diseases, including some kinds of cancer.
Some genes (parts of our DNA) contain instructions for controlling
when our cells grow and divide. 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.
Cancers can be caused by DNA mutations (defects) that activate oncogenes
or inactivate tumor suppressor genes. Some people with cancer have
DNA mutations that they inherited from a parent. These mutations
increase their risk for the disease. Usually, however, DNA mutations
are acquired during life rather than inherited before birth.
The DNA mutations that cause some inherited forms of bone cancers
are known. The Li-Fraumeni syndrome is caused by inherited mutations
that inactivate the p53 tumor suppressor gene. This results in a
very high risk of developing one or more types of cancer that include
breast cancer, brain cancer, osteosarcoma, and other sarcomas. Inherited
defects of the Rb tumor suppressor gene increase the risk of developing
retinoblastoma, a type of eye cancer that affects children. Children
with this defect also have an increased risk for developing osteosarcoma.
When children inherit Rb or p53 mutations from a parent, these mutations
are present in every cell of their body and, therefore, can be detected
by testing DNA of blood cells. Because every person has two p53
and two Rb genes but passes only one of each to their children (the
other gene comes from their mate), the odds that a parent will pass
their mutated gene on to a child are 1 out of 2.
The majority of bone cancers are not caused by inherited DNA mutations.
They are the result of mutations acquired during the person's lifetime.
These mutations are present only in the cancer cells and are not
passed on to the patient's children. Although radiation is very
useful in treating some forms of cancer, it can also cause cancer
by damaging DNA. This is why bones exposed to radiation as a treatment
for other cancers are more likely to develop bone cancer later in
the patient's lifetime.
Other DNA mutations have no apparent cause but may result from random
errors that occur when cells reproduce. Before a cell divides, it
must copy its DNA so that both new cells have the same set of instructions.
Sometimes this copying process is not completely accurate. Scientists
still do not know exactly why or how these mutations happen to some
people but not to others.
Fortunately, cells have ways of "proofreading" DNA copies
and repairing any errors. But when cells divide shortly after their
DNA is damaged, new "daughter cells" may be formed before
the original cell has time to repair its DNA damage. Once the cells
are formed, it is too late to repair the damage. The result is that
cell instructions for growth control can be permanently altered,
and a cancer (such as osteosarcoma) may develop. This is why normal
situations (such as the teenage growth spurt) and diseases (such
as Paget disease of bone, multiple exostoses, and multiple osteochondromas)
causing rapid bone growth increase the risk of developing osteosarcoma.
Although scientists are making progress in understanding this process,
there are still some points that are not completely understood.
As their knowledge increases, they hope to develop ways to better
prevent and treat bone cancers