Hemangiosarcoma in Dogs: A Helpful Guide


Canine cancer remains one of the most prominent causes of deaths in dogs. Cancer has become incredibly common, particularly in older dogs. In fact, an estimated 50 percent of dogs over 10 years of age develop some form of cancer at some point. This high rate is an effect of providing dogs with better care, prolonging their lives to a point where they can more easily succumb to cancer.

One of the most predominant forms of canine cancer is hemangiosarcoma. Read on to learn more about hemangiosarcoma, some signs and symptoms to look out for, and effective treatment options that you should look into.

What is Hemangiosarcoma?

Hemangiosarcoma, which is also known as angiosarcoma or malignant hemangioendothelioma, is a cancer that originates in your dog’s endothelium. The endothelium comprises the top layer of tissue surrounding your dog’s blood vessels, lymph nodes, and heart.


Hemangiosarcoma invades your dog’s blood vessels and can essentially appear in any tissue that has blood vessels (meaning just about anywhere in the body). Because this form of cancer is based in blood vessels, any diagnosis should be treated seriously. Hemangiosarcoma tumors are often filled with blood, so a ruptured tumor can lead to various health problems related to internal and external bleeding.

Types of Hemangiosarcoma in Dogs

There are three main forms of hemangiosarcoma found in dogs:

Dermal Hemangiosarcoma

This form of hemangiosarcoma appears on the skin. It is the easiest to surgically remove and has the highest chances of complete recovery. However, it still poses a potential threat as about one third of cases may become malignant and metastasize internally.

Dermal hemangiosarcoma tumors appear as red or sometimes black growths on your dog’s skin. This form of hemangiosarcoma is most often associated with exposure to the sun, so it will more likely form on areas that are naked or lightly furred, like the abdomen. Dogs with short white fur are most susceptible to dermal hemangiosarcoma.

Subcutaneous (or Hypodermal) Hemangiosarcoma

Where dermal hemangiosarcoma affects the surface of skin, subcutaneous hemangiosarcoma occurs under the top layer of skin. Hypodermal hemangiosarcomas appear as dark red blood growths under the skin. About 60 percent of subcutaneous hemangiosarcomas metastasize and spread internally.

Visceral Hemangiosarcoma

Visceral hemangiosarcomas account for 2 percent of all malignant tumors in dogs. It most often affects the spleen and the heart.

  • Splenic hemangiosarcoma – The spleen isn’t essential to life, but it does serve important roles in your dog’s blood and lymph nodes. Tumors forming on the spleen often tend to break and bleed profusely, benign or not. Removing the spleen may potentially prevent this life-threatening bleed out. Prior to a splenectomy, it may be difficult for your veterinarian to determine if the mass is malignant or benign. An estimated 25 percent of dogs with a splenic hemangiosarcoma have been found to also have a heart-based hemangiosarcoma.
  • Heart-based hemangiosarcoma – Viscerla hemangiosarcoma may also affect the heart. Similar to splenic hemangiosarcoma, heart-based hemangiosarcoma may pose a danger due to rupturing and bleeding. The heart is enclosed in a sac of tissue called the pericardium. If the hemangiosarcoma growth ruptures or begins to bleed, it can fill the pericardium, putting extra pressure on your dog’s heart and preventing it from pumping properly. This condition is known as pericardial effusion and can lead to some serious health complications.

Some cases also report hemangiosarcoma affecting the:

  • Liver
  • Lungs
  • Oral cavity
  • Kidneys
  • Muscle tissue
  • Bone
  • Uterus
  • Urinary bladder


Symptoms of Hemangiosarcoma in Dogs

Symptoms for hemangiosarcoma differ based on the dog, the location, and type of hemangiosarcoma. As most occur in internal organs, most dogs will show very few or no serious symptoms until it’s too late. Some of the most common symptoms include:

  • A lump under the skin
  • Getting tired or fatigued easily
  • Visible bleeding, including in the form of nosebleeds
  • Pale colored gums
  • Sudden unexplained weakness
  • Swelling in the abdomen
  • Breathing difficulties
  • Depression
  • Seizures
  • Collapsing
  • Abnormal heart rhythms

Hemangiosarcoma occurring in the skin will usually give way to a mass or lump that you can feel under the skin. The lump may bleed or become ulcerated. Tumors occurring in or on bone can cause pain and discomfort. In certain locations, like the ribs, you should be able to feel the lump as a firm swelling.

A hemangiosarcoma spleen or liver tumor in dogs will often only show clinical symptoms when the tumor has ruptured and bled in your dog’s abdomen. This bleeding can lead to:

  • Weakness
  • Anemia
  • Collapse, if the bleeding is severe
  • Gums that look pale or white

A hemangiosarcoma tumor in the heart can cause:

  • Weakness
  • Breathing difficulties
  • Intolerance to exercise and physical activity
  • Fluid building up in the abdomen

Most of these cancer signs in dogs are caused by pericardial effusion.

Some other general symptoms for visceral hemangiosarcoma include:

Causes of Hemangiosarcoma in Dogs

The exact cause of hemangiosarcoma is hard to spot. It is likely tied to genetics and environmental factors. Dermal hemangiosarcoma has been found to be associated with excessive exposure to sunlight.=

In humans, certain chemicals like vinyl chloride have been associated with the development of certain cancers. Hemangiosarcoma is rare in humans, so there isn’t much research about it or its precise causes.


Risk Factors for Hemangiosarcoma in Dogs

Hemangiosarcoma is more common in dogs than any other animal species, humans included. It is most often found in dogs that are middle-aged or older, usually between 6 and 13 years old. However, hemangiosarcoma has been found in puppies less than year old. Male dogs also seem to have a higher chance of occurrence than female dogs.

This form of cancer also seems to be more common in medium and large sized dog breeds, particularly:

Hemangiosarcoma of the spleen is the most common form of this canine cancer. However, due to the aggressive nature of the cancer and its origin in blood vessels, hemangiosarcoma usually spreads to the heart, lungs, liver, and spleen.

Diagnosing Canine Hemangiosarcoma

Diagnosis starts with a basic physical examination to evaluate your dog’s health. This will often include examining your dog’s mucus membranes for potential anemia. In the gums, this may manifest in a pale or white color. Your dog’s vet will also feel the abdomen for lumps or swelling, draw blood to determine if your pup is properly forming clots, and aspirate fluid to see if there’s any blood in the abdomen.

Your vet will also perform a complete blood test to detect signs of anemia or low blood platelet counts. These tests include urinalysis, chemical blood profiles, and a complete blood count.

One of the best ways to see what’s happening in the abdominal cavity is to use diagnostic imaging. X-rays can be used to see masses in the abdomen along with any potential fluids leaking into the abdomen. Your vet may also use thoracic radiography to determine if any cancer cells have metastasized into the lungs. Ultrasonograms may reveal any tumors in the spleen or liver, while your vet can perform an echocardiogram to detect masses in your dog’s heart.

To get a definitive diagnosis, your vet will need to perform a biopsy, which involves taking tissue from the tumor or any affected areas for analysis. This can prove difficult as the best results come from the primary tumor, which may be challenging to determine or find if there are multiple tumors.

Treatments for Hemangiosarcoma in Dogs

Treatments differ based on the location of the hemangiosarcoma and the extent to which it has spread. Dermal hemangiosarcomas are much easier to treat than those affecting internal organs. Most hemangiosarcomas on the skin can be treated through surgical removal of the tumor.

If the vet is unable to remove the hemangiosarcoma completely or suspects some of the cancerous cells have spread into the muscles or subcutaneous tissue, they may also use chemotherapy. Radiation therapy, alone, or in conjunction with other treatments, has also been found to be effective in treating hemangiosarcoma.


Visceral forms of hemangiosarcoma are much harder to treat and require more aggressive methods and procedures. With splenic hemangiosarcoma, the vet may be able to remove the spleen entirely if the tumor has been identified early. The vet can also remove tumors near the heart. Both procedures may prolong your pup’s life. If there is fluid built up around the heart, the vet can perform a pericardial tap or remove the pericardial sac entirely.

Surgery alone is rarely helpful with visceral hemangiosarcoma because of its highly aggressive nature. Most visceral hemangiosarcomas will have spread by the time they have been properly diagnosed. For maximum effect, your vet will combine surgery with chemotherapy as standard treatment. The recommended chemotherapy is single-agent doxorubicin, administered intravenously every 3 weeks. Other common chemotherapy medications include:

  • Doxorubicin
  • Cytoxan
  • Cyclophosphamide
  • Vincristine

Other treatments aim to soothe symptoms, cure bleeding disorders, and provide other supportive care to prolong your dog’s life and ensure comfort.

Preventing Hemangiosarcoma in Dogs

Much of prevention for hemangiosarcoma centers on its dermal form. The best way to prevent dermal hemangiosarcoma is to limit direct exposure to the sun, particularly if your pup has light skin, short hair, or a particularly thin haircoat.

Provide plenty of shade and apply dog-safe sunscreen to sun-sensitive areas of the body, like the nose, groin, belly, tips of the ears, and around the lips. If your dog will be exposed to the sun for extended periods of time during peak hours, reapply sunscreen regularly.

There is no known way to prevent any internal form of hemangiosarcoma. It will certainly help to feed your pup a healthy, balanced, nutrient-rich diet with plenty of fresh water. Above all, make sure you keep up with regular checkups and vaccination shots. Blood work, urinalysis, and physical exams performed regularly allow you to properly identify diseases and disorders before you even notice any symptoms.

Above all, make sure you examine your furry companion yourself and don’t forget to check for signs of dog skin cancer like melanoma. You know your dog better than anyone and probably know when he’s not feeling well or seems a little off. Take your dog to the vet as soon as you notice any problems. The sooner your dog is treated, the better chances of his better health and wellbeing.



  1. “Hemangiosarcoma.” The National Canine Cancer Foundation, Accessed 3 May 2017. www.wearethecure.org/learn-more-about-canince-cancer/canine-cancer-library/hemangiosarcoma/.
  2. “Hemangiosarcoma in Dogs – Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost.” WagWalking, 30 Sept. 2015, Accessed 3 May 2017. www.wagwalking.com/condition/hemangiosarcoma.
  3. “Liver and Spleen Cancer (Hemangiosarcoma) in Dogs.” PetMD, Accessed 3 May 2017. www.petmd.com/dog/conditions/cancer/c_dg_cancer_spleen_liver.
  4. “Hemangiosarcoma in Dogs.” PetMD, Accessed 3 May 2017. www.petmd.com/blogs/fullyvetted/2012/july/hemangiosarcoma_in_dogs-26511.
  5. “The Silent Killer: Hemangiosarcomas or a Ruptured, Bleeding Spleen in Dogs.” PetHelpful, Accessed 3 May 2017. www.pethelpful.com/dogs/Dog-Ruptured-Bleeding-Tumor-on-Spleen-the-Silent-Killer.

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