Hemangiosarcoma in Dogs

Causes, Treatment, and Prevention

Tired Golden Retriever lying on wooden floor
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Affecting dogs more than humans and other animals, hemangiosarcoma is a type of cancer that can become very serious and spread quickly throughout the body. Like many other cancers that affect dogs, hemangiosarcoma causes tumors, but it can affect many different body parts. Growths typically occur in the spleen, liver, heart, and skin. Any dog can develop this disease, but breeds including golden retrievers, German shepherds, and Labrador retrievers are the most diagnosed.

This canine cancer can be either external or internal, appearing as abnormalities on the skin or more serious symptoms like weakness, a bloated abdomen, pale gums, or even collapse. The signs of internal hemangiosarcoma can be similar to those of other serious diseases, so if your dog shows any symptoms, it's important to get to a veterinarian right away. External hemangiosarcoma may be caused by sun exposure, but the internal variation has no known cause. This disease can be fatal, so treatment should start as early as possible.

What is Hemangiosarcoma?

Hemangiosarcoma is a cancer of the endothelial cells—which line the interior of the blood vessels—that causes tumors that are highly malignant, may occur rapidly, and are metastatic (spreading to other parts of the body). Hemangiosarcoma growths most commonly occur in the spleen, liver, heart, and skin, with skin symptoms being related to external hemangiosarcoma.

Tumors on the spleen and liver may bleed or rupture, which may cause the abdominal cavity to fill with blood (hemoabdomen). Tumors in the heart most commonly appear in the right atrium and also tend to bleed. Blood fills up the sac around the heart (pericardium) and impairs cardiac function. Hemangiosarcoma tumors that affect the heart can cause heart failure and reflect those symptoms.

Hemangiosarcoma can also develop on the skin (dermal) or under the skin (subcutaneous). Dermal tumors are typically raised bumps that can be red, purple, and/or black. They may eventually ulcerate and bleed. Subcutaneous tumors are very malignant and likely to spread. Subcutaneous hemangiosarcoma may not be visible to the naked eye until it begins bleeding, which may look like a deep, spreading bruise.

Symptoms of Hemangiosarcoma in Dogs

Internal tumors (in the spleen, liver, or heart) may not cause symptoms at first. Signs may appear vague to begin, then suddenly get worse due to rupture and/or bleeding of the tumor. Internal hemangiosarcoma symptoms are often the same as signs of internal bleeding and heart disease. They can include:


  • Lethargy and weakness (constant or intermittent)
  • Distended abdomen (bloated appearance of belly)
  • Pale gums or mucous membranes
  • Collapse
  • Bruising, bleeding, lumpy, or ulcerated skin

Lethargy and Weakness

Like humans, dogs can become lethargic when they don't feel well, but this is often accompanied by weakness in dogs with hemangiosarcoma. Affected dogs may appear especially weak when standing up from laying down or after light exercise.

Distended Abdomen

Abdominal distension looks like the dog's stomach is bloated as it fills with fluid. In dogs with hemangiosarcoma, this is caused by tumors that affect the major organs.

Pale Gums or Mucous Membranes

Pale gums can indicate a variety of different medical conditions, but if your dog's gums are any color other than pink, veterinary attention is always necessary. In dogs with hemangiosarcoma, this is typically caused by blood loss in the abdomen or space around the heart due to tumors.


Like pale gums, collapse is another sign of serious heart disease. Hemangiosarcoma can cause many similar symptoms in dogs as heart disease because of tumors that grow inside the body near (or on) the heart. Your dog may lose consciousness when heart problems cause a lack of blood flow to the brain.

Bruising, Bleeding, Lumpy, or Ulcerated Skin

Skin tumors are a symptom of external hemangiosarcoma, which affects the blood vessels of the skin. This can appear as a bruise which may develop into a lumpy area, and it can bleed or become ulcerated as the disease progresses. External hemangiosarcoma may be more likely in light-colored dogs or those with sparse fur that makes the skin more susceptible to sun exposure.

Causes of Hemangiosarcoma

The two types of hemangiosarcoma have different causes. This disease can affect dogs of any age, but it typically occurs in middle-aged and senior dogs. Causes may include:

  • Sun exposure: Hemangiosarcoma of the skin is typically caused by too much sun exposure. Tumors usually occur on hairless areas of the skin or areas with white hair.
  • Genetics: The cause of internal hemangiosarcomas is not fully known, and any breed of dog can get this type of cancer. However, certain breeds appear to have a genetic predisposition. These include golden retrievers, German shepherds, and Labrador retrievers.

Diagnosing Hemangiosarcoma in Dogs

Take your dog to your veterinarian if you notice skin bumps, symptoms of internal hemangiosarcoma, or any other signs of canine illness for them to properly diagnose the condition. If hemangiosarcoma is suspected, your veterinarian will begin by discussing your dog's history and performing a full physical examination. Abdominal masses may or may not be palpable during the exam. If there is blood or other fluid in your dog's abdomen, your vet might be able to feel it through the body. Heart tumors may cause abnormal heart sounds that can be heard with a stethoscope.

The next diagnostic steps include full lab work (complete blood count, blood chemistry, urinalysis) and radiographs (X-rays) of the chest and abdomen. Your vet will be looking for lab abnormalities that can indicate cancer as well as visible tumors or abnormalities in the chest and abdomen. Bloodwork will help your veterinarian determine your dog's blood cell count, blood clotting ability, and organ function to narrow down the cause of its illness.

Skin tumors can often be aspirated or biopsied, which involves your veterinarian taking a sample to be reviewed under a microscope. Samples are sent to a pathologist to look for microscopic cancer cells. Internal tumors may also be aspirated or biopsied if your veterinarian deems it safe for your dog. If your dog has fluid in its abdomen, this may also be collected and sent to a lab for analysis.

In some cases, a definitive diagnosis of hemangiosarcoma cannot be made until the tumor is surgically removed and sent to a pathologist. Depending on the diagnosis, your primary veterinarian may refer you to a veterinary oncologist and/or veterinary surgeon for treatment.


The first step to treat hemangiosarcoma in dogs is to surgically remove the primary tumor, if possible. Surgery for splenic tumors typically involves complete removal of the spleen (which your dog can live healthily without). Tumors that cannot be fully removed may be debulked as much as possible. Some tumors are inoperable, especially those in the heart.

Surgical removal of skin hemangiosarcomas is usually curative if the entire tumor is removed and there is no metastasis.

Staging is an important part of both the diagnostic and treatment process. Dogs will need full lab work, radiographs of the chest and abdomen, and possibly advanced imaging like CT or MRI. This allows the vet to see where cancer has spread in the body, then formulate the best possible treatment plan.

Chemotherapy is often recommended for dogs following surgery, especially if the mass could not be completely removed or if metastasis is present. A veterinary oncologist will develop a chemotherapy protocol that is best for your dog, but a medication called doxorubicin (Adriamycin) is the most common treatment. This usually involves visits to the vet for chemotherapy injections every two to three weeks for several months.

Palliative radiation therapy may be recommended to reduce pain and provide a better quality of life when other treatments are not effective or if no other treatment options exist.

Prognosis for Dogs With Hemangiosarcoma

Unfortunately, dogs with internal hemangiosarcoma usually do not survive this disease. When surgery and chemotherapy are performed, most dogs typically live between five and seven months, and only 10 percent survive for a year or more. Medications can be provided by veterinarians to help these dogs remain as comfortable as possible during treatment.

The prognosis for dogs with hemangiosarcoma of the skin depends on the type and size of tumor they're affected with. Not all external tumors will continue to spread after being surgically removed, and dogs with these tumors may remain cancer-free after undergoing the proper procedures.

How to Prevent Hemangiosarcoma in Dogs

Since most types of hemangiosarcoma cannot be prevented, early detection is the next best option. External hemangiosarcoma may be prevented through lifestyle management, and internal forms of this disease should be prevented through selective breeding:

Early Detection

The sooner cancer is detected in a dog, the better its chances are of successful treatment. This is why it's so important to follow your vet's recommendation for annual or biannual wellness exams and routine screening laboratory tests.

Sun Exposure (External Hemangiosarcoma)

Hemangiosarcoma of the skin may be prevented by minimizing your dog's sun exposure. If your dogs have light-colored or sparsely coated fur, it's essential to monitor their time outside. Those with thin fur, in particular, should have sunscreen applied before any extended periods of time spent outdoors (and some breeds with especially short or sparse fur can benefit from daily applications).

Selective Breeding

Internal hemangiosarcoma is more difficult to prevent than external variations. Dogs with a history of hemangiosarcoma should not be used for breeding purposes, and selective breeding is a very effective way to help stop the spread of this disease. However, many dogs are bred earlier in life before they develop hemangiosarcoma. Responsible breeders should provide the medical history for each of their litters, with a few generations of history being best to determine the risk of puppies getting cancer.

Article Sources
The Spruce Pets uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Hemangiosarcoma in Dogs. Colorado State University Flint Animal Cancer Center.

  2. Visceral Vascular Tumors. VCA Animal Hospitals.

  3. Diagnosis of Cardiovascular Disease in Dogs. Merck Veterinary Manual.

  4. Vascular Tumors Affecting the Skin. VCA Animal Hospitals.