How does cancer spread?
What is metastasis?
Metastasis refers to the spread of cancer from one organ to another. Normal cells (with the exception of blood cells)
typically adhere to each other, but malignant cancer cells gain the ability to break away from the primary tumor (the very
first tumor that formed), to travel throughout the body via the bloodstream or lymphatic system, and to initiate new growths
at these distant sites.
When cancer cells spread and form a new tumor in a different organ, the new tumor is referred to as a metastatic tumor.
The cells in the metastatic tumor come from the original tumor. This means that if, for example, stomach cancer spreads to
the liver, then the metastatic tumor in the liver is made up of cancerous stomach cells (not liver cells). In this case, the
disease in the liver would be called metastatic stomach cancer, and not liver cancer.
Where does cancer spread?
Cancer cells can spread (metastasize) to almost any other organ, commonly the lungs, bones or liver. Some cancers tend
to spread to certain organs, however, each cancer has the ability to spread to any organ throughout the body.
Are there symptoms of metastatic cancer?
Some pets with metastatic cancer may not have obvious symptoms but if they do, the type and frequency of the symptoms
will depend on the extent and location of the metastasis. For example, cancer that spreads to the bones is likely to cause
pain and can lead to bone fractures, or cancer that spreads to the brain can cause symptoms such as seizures.
Sometimes a pet’s primary cancer is discovered only after the metastatic tumor causes symptoms. For example, a pet
whose stomach cancer has spread to the liver may experience abdominal swelling or jaundice (yellowing of the skin) before
experiencing any symptoms from the primary tumor in the stomach.
How do we know whether a cancer is a primary or a metastatic tumor?
To determine whether a tumor is primary or metastatic, a pathologist (a doctor who specializes in disease diagnosis)
examines a tumor sample under the microscope and performs a variety of specialized diagnostic tests. Cancer cells often
look like abnormal versions of cells in the tissue from which they developed (eg breast cancer cells may still resemble in
appearance normal breast cells), and it may be possible to tell where the cancer cells came from.
If my pet is diagnosed with metastatic cancer, can the primary tumor be found?
When a metastatic tumor is found first, the primary tumor can be found in many cases using diagnostic procedures, such
as laboratory tests or imaging studies. However, in some cases, the primary tumor cannot be found despite extensive tests.
The pathologist will know if the tumor is metastatic if the cells do not resemble the cells found in the organ or tissue from
which the tumor came. Veterinarians then refer to the primary tumor as unknown, and the pets are said to have cancer of
unknown primary origin.
Metastasis refers to the spread of cancer from one organ to another. Normal cells (with the exception of blood cells)
typically adhere to each other, but malignant cancer cells gain the ability to break away from the primary tumor (the very
first tumor that formed), to travel throughout the body via the bloodstream or lymphatic system, and to initiate new growths
at these distant sites.
When cancer cells spread and form a new tumor in a different organ, the new tumor is referred to as a metastatic tumor.
The cells in the metastatic tumor come from the original tumor. This means that if, for example, stomach cancer spreads to
the liver, then the metastatic tumor in the liver is made up of cancerous stomach cells (not liver cells). In this case, the
disease in the liver would be called metastatic stomach cancer, and not liver cancer.
Where does cancer spread?
Cancer cells can spread (metastasize) to almost any other organ, commonly the lungs, bones or liver. Some cancers tend
to spread to certain organs, however, each cancer has the ability to spread to any organ throughout the body.
Are there symptoms of metastatic cancer?
Some pets with metastatic cancer may not have obvious symptoms but if they do, the type and frequency of the symptoms
will depend on the extent and location of the metastasis. For example, cancer that spreads to the bones is likely to cause
pain and can lead to bone fractures, or cancer that spreads to the brain can cause symptoms such as seizures.
Sometimes a pet’s primary cancer is discovered only after the metastatic tumor causes symptoms. For example, a pet
whose stomach cancer has spread to the liver may experience abdominal swelling or jaundice (yellowing of the skin) before
experiencing any symptoms from the primary tumor in the stomach.
How do we know whether a cancer is a primary or a metastatic tumor?
To determine whether a tumor is primary or metastatic, a pathologist (a doctor who specializes in disease diagnosis)
examines a tumor sample under the microscope and performs a variety of specialized diagnostic tests. Cancer cells often
look like abnormal versions of cells in the tissue from which they developed (eg breast cancer cells may still resemble in
appearance normal breast cells), and it may be possible to tell where the cancer cells came from.
If my pet is diagnosed with metastatic cancer, can the primary tumor be found?
When a metastatic tumor is found first, the primary tumor can be found in many cases using diagnostic procedures, such
as laboratory tests or imaging studies. However, in some cases, the primary tumor cannot be found despite extensive tests.
The pathologist will know if the tumor is metastatic if the cells do not resemble the cells found in the organ or tissue from
which the tumor came. Veterinarians then refer to the primary tumor as unknown, and the pets are said to have cancer of
unknown primary origin.
© 2007 Pet Cancer Center. ALL RIGHTS RESERVED.
Last updated 1/8/08
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How does cancer spread?
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