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,