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Hemangiosarcoma is an aggressive, malignant tumor that affects the blood vessels lining cells. Although hemangiosarcoma could theoretically arise from any tissue where there are blood vessels, the most common location is the spleen. Other primary locations include the heart, liver, skin and bone. These tumors are typically classified as dermal, subcutaneous or hypodermal, and visceral.

Dermal hemangiosarcoma is associated with sun exposure. It is uncertain what causes other types of hemangiosarcoma, but in humans exposure to certain chemicals, such as vinyl chloride, has been implicated. Because of the increased incidence in several breeds, a genetic link appears to be one of several likely causes. Hemangiosarcoma is rarely found in humans, so little research has been done, and the amount of information about the cause of this tumor is somewhat limited.


  • Lump under the skin
  • Abdominal swelling
  • Visible bleeding
  • Seizures
  • Easily tired
  • Abnormal heart rhythms
  • Unexplained weakness
  • Collapse
  • Pale color in the gums
  • Depression
  • Difficulty breathing

Hemangiosarcoma most often develops in internal organs, and therefore, a dog may have few or no obvious symptoms before the onset of severe clinical signs of disease.

Breeds at Risk

Hemangiosarcoma is more common in dogs than in any other species. It usually occurs in middle-aged to older dogs, 6 to 13 years old, although it has been seen in dogs younger than one year. It tends to develop in mid-size to large breeds.

  • Boxers
  • German Shepherds 
  • Doberman Pinschers
  • Golden Retrievers
  • English Setters
  • Labrador Retrievers


To diagnose hemangiosarcoma, a veterinarian will begin with a thorough examination, which may include looking at the mucous membranes for signs of anemia (pale gums), feeling for abdominal swelling, aspirating fluid from the abdomen to see if blood is present and drawing blood to see if clots form.

Further diagnostic workup will most likely include a complete blood count, chemistry panel, urinalysis and x-rays of the chest and abdomen to determine the extent of organ involvement and whether the tumor has metastasized. A biopsy or removal of the tumor is required for definitive diagnosis, but this can be challenging because a dog may have multiple tumors and/or the primary tumor site may be difficult to determine. Severe hemorrhage is also a significant risk during these surgical procedures.


Treatment depends on the location of the tumor and is more successful when this cancer occurs on the skin than when it is found in an internal organ. Many small dermal hemangiosarcomas can be successfully treated and cured through surgical removal of the tumor.

If the veterinarian cannot remove the entire skin tumor or it has penetrated into the subcutaneous tissue or muscles below the skin, chemotherapy is often added to the treatment regimen. Radiation therapy is also used to treat dermal hemangiosarcoma.

Tumors in the internal organs require more aggressive treatment and are less likely to be cured. Removal of the spleen can prolong a dog’s life if the tumor is located in the spleen or near the heart and is still small. Hemangiosarcoma in the internal organs is highly aggressive, and most tumors have spread by the time they have been diagnosed, so surgery is combined with chemotherapy. Many chemotherapy protocols are available, and they may include the following drugs: cyclophosphamide, vincristine, doxorubicin and cytoxan.


With the exception of the skin form of hemangiosarcoma, a diagnosis of hemangiosarcoma is serious because these cancers spread quickly. The disease is rarely curable, and long-term prognosis is poor. Also, because these tumors start in blood vessels, they are frequently filled with blood, and when a blood-filled tumor ruptures, it can cause internal or external bleeding.

Dogs with internal organ involvement who are treated with surgery alone live an average of only 3 months. Dogs without identifiable metastasis at the time of surgery and who are treated with chemotherapy may survive for approximately 6 months.

Hemangiosarcoma is generally accompanied by a blood-clotting disorder that may complicate surgical procedures and postoperative recovery.

Current Research

Click here to find out about Morris Animal Foundation--funded research into hemangiosarcoma.

Morris Animal Foundation urges pet owners not to implement any suggestions on animal health treatments without prior consultation with their licensed veterinarian. If your pet is experiencing health issues, contact your licensed veterinarian. The Foundation funds research to enhance medical options available to veterinary professionals and their patients.