Hemangiosarcoma in the Dog

Hemangiosarcoma is an aggressive cancer that arises from blood
vessels. The cancer can be found anywhere in the body (because
blood vessels occur throughout the body). Hemangio-sarcoma is
most commonly found in the spleen, liver, and heart. Prognosis
is determined by the location of the disease. Although any breed
of dog can develop hemangiosarcoma, certain breeds of dogs
appear to be at higher risk, such as the German Shepherd,
English Setter, and Golden Retriever. We do not know what
triggers the growth of this type of cancer. Symptoms of
hemangiosarcoma are usually determined by the location of the
disease. Many dogs with the cancer in an internal organ show
signs of intermittent or persistent weakness or even collapse.
This is due to a variety of factors. Because the cancer is
producing abnormal blood vessels, these vessels tend to be very
weak and prone to leaking. Further growth leads to rupture of
one of these cancerous vessels, resulting in loss of blood.

As the spleen is the internal organ most commonly affected by
this cancer and is an organ that filters the blood, if one of
the abnormal blood vessels ruptures, this allows the “spilling”
of blood from the spleen into the abdominal cavity. Rapid loss
of blood causes weakness or collapse. If only a small amount of
blood is lost, the episode of weakness can be transient, as that
blood can be reabsorbed into the body. If a large amount of
blood is lost, the weakness is so profound that the dog may
collapse. This can be an emergency situation. Distention of the
belly may also be observed because of the large volume of free
blood in the abdominal cavity.

If the cancer is on the heart, this bleeding occurs into the sac
that surrounds the heart, resulting in a compromise of the
heart’s ability to pump blood effectively. This also can cause
weakness and potential collapse.

A further problem exists when the cancerous blood vessel
ruptures. The release of blood into a body cavity carries with
it cancer cells, effectively resulting in bathing of the cavity
with cancer cells. This, along with the ease with which cancer
cells break off from the abnormal blood vessels and thus gain
access to the rest of the body through the bloodstream, results
in rapid dissemination of cancer throughout the body. This
spread of cancer to distant sites is termed “metastasis.” It is
this widespread metastasis that makes hemangiosarcoma so
“aggressive” and bad. Often the cancer has metastasized before
any clinical signs are evident.

When hemangiosarcoma is diagnosed (or suspected), a number of
diagnostic tests will be performed to stage your dog’s cancer.
Staging allows your veterinarian and the veterinary oncologist
to educate you further about your dog’s disease, allowing you to
make informed decisions regarding treatment. A chest x-ray will
be performed to evaluate the size of the heart and the lungs and
look for metastasis. A complete blood count, chemistry profile,
and urinalysis will be obtained to assess your dog’s overall
health status.

We may perform a coagulation blood panel to evaluate the ability
of your dog’s body to clot blood. We may also perform an
ultrasound examination of the abdomen and! or the heart in
search of metastasis. Other tests may be recommended, depending
on individual circumstances. Treatment for hemangiosarcoma
involves two different modalities. The first is often surgery to
remove the primary tumor. Sometimes, if multiple sites of
metastases are found during the diagnostic testing, surgery will
be of no benefit. Whenever we are dealing with cancers that have
a high potential to metastasize, we use chemotherapy.
Fortunately, chemotherapy in dogs and cats is very different
from “chemo” in people. Because our focus is on quality of life
for our pets, this is an important factor; we never want the
treatment to be worse than the disease. There are various
reasons why chemo is better tolerated in pets, but the most
important factor is psychologic. Your dog does not know he has
cancer. He also does not know the drugs make people sick, so he
does not anticipate that he will get sick. Human cancer patients
suffer from a phenomenon called anticipatory vomiting, but dogs
do not have this problem. This is not to say that some dogs may
not have any side effects caused by the chemo, but in the few
dogs that do show side effects, the signs are typically mild and
transitory.

Most breeds of dogs do not lose their hair (they have fur, which
grows differently from hair). Your veterinarian or cancer
specialist will discuss possible side effects with you at
greater length. Unfortunately, hemangiosarcoma is not curable.
Dogs with internal organ involvement who are treated with
surgery live an average of only 2 months. Dogs who do not have
identifiable metastasis at the time of surgery and who are
treated with chemotherapy live a median of 6 to 10 months.
(Median survival means that 50 per cent of dogs live less than
this time and 50 per cent live longer.) Some dogs with
demonstrable metastasis may also respond to chemotherapy,
providing a prolonged quality of life compared with dogs that
are not treated at all. Dogs with this type of cancer located in
the subcutaneous tissues (just under the skin) live a median of
about 6 months with surgery alone. No studies have been
performed on use of chemotherapy for this anatomic location.

Hemangiosarcoma can also occur on the skin of dogs. This appears
to be a form of cancer induced by exposure to the sun and
carries a much better prognosis than the internal form of the
disease. Surgical removal of the skin form, provided it did not
arise as a metastasis from the more aggressive form, provides a
disease-free interval of about 1.5 years. New lesions can
continue to form, however, because of previous or continued sun
damage and exposure.

New types of treatments are being investigated continuously in
the hope of improving the response rate of dogs with this
disease. Again, quality of life is always the main goal, and
this can often be achieved by working closely with your
veterinary team.

The above is general veterinary information. Do not begin
any course of treatment without consulting your regular
veterinarian. All animals should be examined at least once every
12 months.