| Metastasis or
"mets":How Cancer Spreads
Copied from then updated:http://www.phoenix5.org/Basics/mets.html
metastasis
(meh-TAS-ta-sis): The spread of cancer from one part of the body to
another. Tumors formed from cells that have spread are called
"secondary tumors" and contain cells that are like those in the
original (primary) tumor. The plural is metastases.
(further resources at the end of this
article)
Tumors are called "malignant" because they have the ability to
invade normal tissues (replacing healthy cells with cancer cells)
and to metastasize (spread) to other parts of the body. Death from
cancer often comes not from the primary site (where the cancer first
began) but from the metastases [also known as "mets"]. For example,
a patient with stomach cancer may actually die from liver failure
after the cancer has spread to that organ.
When a certain type of cancer spreads to another part of the body,
it does not change its type. For example, if a person with a
lymphoma develops a tumor in the lung which is a metastasis from
this lymphoma, the tumor growing in the lung has the same
characteristics as the lymphoma. It does not represent a new lung
cancer of the type which would develop if the cancer was to start
in, or to be "primary" in the lung. It is important to understand
this as the treatment that will be effective against the metastasis
will be the same treatment that will be used for the primary
lymphoma. This is why it is most important for the doctors treating
a patient to be able to establish the primary site at which any
cancer originated.
Metastases takes place in many ways: through the lymphatic system,
through the bloodstream, by spreading through body spaces such as
the bronchi or abdominal cavity, or through implantation.
The most common way for cancer to spread is through the lymphatic
system. This process is called "embolization". The lymph system has
its own channels that circulate throughout the body, similar to the
veins and arteries of the bloodstream. These channel are very small
and carry a tissue fluid called lymph throughout the body.
Often when a solid tumor is removed by surgery, the surgeon will
remove not only the tumor but the neighboring lymph glands, even
though there is no visible sign of cancer in those glands. This is
done as a precautionary measure, because if even one cell has broken
away from the tumor and lodged in the lymphatic system, the cancer
could continue growing and metastasizing.
Cancer can also metastasize through the bloodstream. Cancer cells,
like healthy cells, must have a blood
supply in order to live, so all cancer cells have access to the
bloodstream. Malignant cells can break off from the tumor and travel
through the bloodstream until they find a suitable place to start
forming a new tumor. (Tumors almost always metastasize through the
veins rather than through the arteries.) Sarcomas spread through the
bloodstream, as do certain types of carcinomas, like carcinoma of
the kidneys, testicular carcinoma, and Wilms' tumor, a type of
kidney cancer seen in young children. Cancers may spread by more
than one route.
Cancers can also spread by local invasion -- that is, by intruding
on the healthy tissue that surrounds the tumor. Some cancers that
spread this way do not venture very far from the original site. An
example of this kind of cancer is basal cell carcinoma of the skin.
When this kind of cancer is removed by surgeon, a wide area of
healthy tissue surrounding it is also removed and it is usually
"cured" immediately. Unless some cells have been left behind, it is
very unlikely that it will recur. (However, it is possible that a
second cancer of the same kind may start to grow at a later time at
a completely different site -- the new growth having nothing to do
with the first.)
A very rare type of metastasis is caused by implantation or
inoculation. This can happen accidentally when a biopsy is done or
when cancer surgery is performed. In this case malignant cells may
actually drip from a needle or an instrument (this is also called a
"spill"). It is desirable, therefore, if possible and if the cancer
is small to remove it completely at the initial surgery -- that is
at the time of the biopsy.
Cancers do not spread in a completely random fashion. Some parts of
the body are more vulnerable to becoming metastatic sites than
others. For example cancers rarely metastasize to the skin, but they
often metastasize to the liver and lungs. Each type of cancer has
its own pattern for metastases.
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