Metastatic Cancer
- What is metastatic
cancer?
Metastatic cancer is cancer that has spread from the place where it first
started to another place in the body. A tumor formed by metastatic cancer cells
is called a metastatic tumor or a metastasis. The process by which cancer cells
spread to other parts of the body is also called metastasis.
Metastatic cancer has the same name and the same type of cancer cells as
the original, or primary, cancer. For example, breast cancer that spreads to
the lung and forms a metastatic tumor is metastatic breast cancer, not lung
cancer.
Under a microscope, metastatic cancer cells generally look the same
as cells of the original cancer. Moreover, metastatic cancer cells and cells of
the original cancer usually have some molecular features in common, such as the
expression of certain proteins or the presence of specific chromosome changes.
Although some types of metastatic cancer can be cured with current
treatments, most cannot. Nevertheless, treatments are available for all
patients with metastatic cancer. In general, the primary goal of these
treatments is to control the growth of the cancer or to relieve symptoms caused
by it. In some cases, metastatic cancer treatments may help prolong life.
However, most people who die of cancer die of metastatic disease.
- Can any type of cancer
form a metastatic tumor?
Virtually all cancers, including cancers of the blood and the lymphatic system (leukemia, multiple myeloma, and lymphoma), can form metastatic tumors. Although rare, the
metastasis of blood and lymphatic system cancers to the lung, heart, central nervous system, and other tissues has been
reported.
- Where does cancer spread?
The most common sites of cancer metastasis are, in alphabetical order, the
bone, liver, and lung. Although most cancers have the ability to spread
to many different parts of the body, they usually spread to one site more often
than others. The following table shows the most common sites of metastasis,
excluding the lymph nodes, for several types of cancer:
Cancer
type
|
Main sites
of metastasis*
|
Bone, liver, lung
|
|
Bone, brain, liver, lung
|
|
Adrenal gland, bone, brain, liver, lung
|
|
Lung
|
Adrenal gland, bone, brain,
liver, other lung
|
Bone, brain, liver, lung,
skin/muscle
|
|
Liver, lung, peritoneum
|
|
Liver, lung, peritoneum
|
|
Adrenal gland, bone, liver,
lung
|
|
Liver, lung, peritoneum
|
|
Bone, liver, lung
|
|
Bone, liver, lung,
peritoneum, vagina
|
*In alphabetical order. Brain includes the neural tissue of the brain (parenchyma) and the leptomeninges (the two innermost
membranes—arachnoid mater and pia mater—of the three membranes known as
the meninges that surround the brain and spinal cord; the space between the arachnoid mater and the pia
mater contains cerebrospinal fluid). Lung includes the main part
of the lung (parenchyma) as well as the pleura (the membrane that covers the
lungs and lines the chest cavity).
- How does cancer spread?
Cancer cell metastasis usually involves the following steps:
o
Local invasion: Cancer cells invade nearby normal tissue.
o
Intravasation: Cancer cells invade and move through the walls of
nearby lymph vesselsor blood vessels.
o
Circulation: Cancer cells move through the lymphatic system and the bloodstream to other parts of the
body.
o
Arrest and extravasation: Cancer cells arrest, or stop moving, in small
blood vessels called capillaries at a distant location. They then invade the
walls of the capillaries and migrate into the surrounding tissue
(extravasation).
o
Proliferation: Cancer cells multiply at the distant location to form small tumors known
as micrometastases.
o
Angiogenesis: Micrometastases stimulate the growth of new blood
vessels to obtain a blood supply. A blood supply is needed to obtain the oxygen
and nutrients necessary for continued tumor growth.
o
1.
Because cancers of the lymphatic system or the blood system are
already present inside lymph vessels, lymph nodes, or blood vessels, not all of
these steps are needed for their metastasis. Also, the lymphatic system drains
into the blood system at two locations in the neck.
The
ability of a cancer cell to metastasize successfully depends on its individual
properties; the properties of the noncancerous cells, including immune
system cells,
present at the original location; and the properties of the cells it encounters
in the lymphatic system or the bloodstream and at the final destination in another
part of the body. Not all cancer cells, by themselves, have the ability to
metastasize. In addition, the noncancerous cells at the original location may
be able to block cancer cell metastasis. Furthermore, successfully reaching
another location in the body does not guarantee that a metastatic tumor will
form. Metastatic cancer cells can lie dormant (not grow) at a distant site for
many years before they begin to grow again, if at all.
2. Does
metastatic cancer have symptoms?
Some
people with metastatic tumors do not have symptoms. Their metastases are found
by x-rays or other tests.
When
symptoms of metastatic cancer occur, the type and frequency of the symptoms
will depend on the size and location of the metastasis. For example, cancer
that spreads to the bone is likely to cause pain and can lead to bone
fractures. Cancer that spreads to the brain can cause a variety of symptoms,
including headaches, seizures, and
unsteadiness. Shortness of breath may be a sign of lung
metastasis. Abdominal swelling or jaundice (yellowing of the skin) can indicate that
cancer has spread to the liver.
Sometimes
a person’s original cancer is discovered only after a metastatic tumor causes
symptoms. For example, a man whose prostate cancer has spread to the bones in
his pelvis may have lower back pain (caused by the
cancer in his bones) before he experiences any symptoms from the original tumor
in his prostate.
3. Can
someone have a metastatic tumor without having a primary cancer?
No. A
metastatic tumor is always caused by cancer cells from another part of the
body.
In most
cases, when a metastatic tumor is found first, the primary cancer can also be
found. The search for the primary cancer may involve lab tests, x-rays,
computed tomography (CT)
scans, magnetic resonance imaging (MRI)
scans, positron emission tomography (PET)
scans, and other procedures.
However,
in some patients, a metastatic tumor is diagnosed but the primary tumor cannot
be found, despite extensive tests, because it either is too small or has
completely regressed. Thepathologist knows that the diagnosed tumor is a
metastasis because the cells do not look like those of the organ or tissue in
which the tumor was found. Doctors refer to the primary cancer as unknown or
occult (hidden), and the patient is said to have cancer
of unknown primary origin(CUP).
Because
diagnostic techniques are constantly improving, the number of cases of CUP is
going down. More information can be found in the Carcinoma
of Unknown Primary Treatment (PDQ®)summary, which is part of NCI’s
comprehensive cancer information database.
4. If a
person who was previously treated for cancer gets diagnosed with cancer a
second time, is the new cancer a new primary cancer or metastatic cancer?
The
cancer may be a new primary cancer, but, in most cases, it is metastatic
cancer.
5. What
treatments are used for metastatic cancer?
Metastatic
cancer may be treated with systemic
therapy (chemotherapy, biological
therapy,targeted
therapy, hormonal
therapy), local therapy (surgery, radiation
therapy), or a combination of these treatments. The choice of treatment
generally depends on the type of primary cancer; the size, location, and number
of metastatic tumors; the patient’s age and general health; and the types of
treatment the patient has had in the past. In patients with CUP, it is
possible to treat the disease even though the primary cancer has not been
found.
6. Are new
treatments for metastatic cancer being developed?
Yes,
researchers are studying new ways to kill or stop the growth of primary
cancer cells
and metastatic cancer cells, including new ways to boost the strength of immune
responses against tumors. In addition, researchers are trying to find ways to
disrupt individual steps in the metastatic process.
Before
any new treatment can be made widely available to patients, it must be studied
in clinical trials (research studies) and found to be safe and effective in
treating disease. NCI and many other organizations sponsor clinical trials that
take place at hospitals, universities, medical schools, and cancer centers
around the country. Clinical trials are a critical step in improving cancer
care. The results of previous clinical trials have led to progress not only in
the treatment of cancer but also in the detection, diagnosis, and prevention of
the disease. Patients interested in taking part in a clinical trial should talk
with their doctor.
No comments:
Post a Comment