Liaison: Jan Young

Email: jannermd@yahoo.com

Canine hemangiosarcoma is a highly malignant, rapidly spreading cancer of the cells that line the blood vessels. As the cancer grows, because it involves the blood vessels, it disrupts blood supply to involved tissue and causes bleeding. Bleeding can be insidious (without symptoms) and chronic for a period of time, or can be sudden and massive resulting in rapid death. Any age or breed of dog can have hemangiosarcoma but it is most common in middle age or older dogs and in large breeds. It is, interestingly, extremely rare in humans and in cats.

Signs and Symptoms

There are three basic forms of hemangiosarcoma and signs and symptoms are related to the form:

  1. Dermal (skin): This involves the blood vessels of the skin, which, in the area of the tumor, become extensive and fragile and eventually bleed, causing swelling, bruising, and/or pain in the area of the tumor, and may cause a more generalized anemia (characterized by fatigue, pale mucous membranes). Bleeding bouts may come and go but once recognized and brought to the attention of a vet, a diagnosis can be made. This is the least severe form of the disease because it is more often (perhaps a third of the time) discovered before metastases occurs and is more amenable to direct treatment.

  2. Hypodermal (below the skin): This is more insidious (without symptoms) allowing the tumor to grow and metastasize without its presence being known. Eventually either this tumor or a metastasis of it will bleed and cause symptoms. If the bleeding occurs in the primary hypodermal tumor, there may be local swelling, discoloration and/or pain, and again, because of the blood loss, there may be more generalized signs of anemia (fatigue, pale mucous membranes). There may be multiple bouts with relative recovery before the dog is brought to a vet and the diagnosis is suspected. As many as two thirds of dogs with hypodermal hemangiosarcomas have visceral metastases at the time of diagnosis, and hence incurable disease.

  3. Visceral (usually spleen or cardiac): Again, early on, there are typically no symptoms, but because of this, once there are symptoms, it is usually because the cancer has spread (metastasized) such that it is incurable. The spleen and heart are the most common organs involved but primary tumors and metastases can and do occur in any blood vessel in the body. Visceral hemangiosarcoma (either primary or metastatic) has the worst prognosis and is almost universally fatal within months, even with aggressive treatment.

Hemangiosarcoma grows rapidly but is painless as it grows and spreads. Eventually there is internal bleeding which can be intermittent and cause brief episodes of pain and/or swelling, and sometimes anemia with paleness of mucous membranes. The dog may recover from these for periods of time. During these times, if the blood loss is great enough, the dog may show signs of fatigue or weakness. And during these times, even though the dog may seem to improve, the cancer is aggressively spreading and metastasizing to other areas of the body. There may be disruptions of organ function such as abnormal heart rhythms, loss of appetite, weight loss, or clotting disorders. Eventually there is rupture of a large tumor, resulting in severe hemorrhage, collapse, shock and even death. By the time of diagnosis, the cancer has almost always spread to the point of being incurable.


The cause of canine hemangiosarcoma is not known but is believed to be, at least in part, genetic because it is so common in dogs and in certain breeds of dog, but not in other animals. Environmental factors also play a role.

Risk Factors

Specific risk factors are not known. Sun exposure can contribute to the development of dermal hemangiosarcoma in light colored dogs with thin coats. Studies are underway to attempt to identify risk factors in high risk breeds.

Diagnostic Tests

Diagnosis is difficult and often occurs too late. Examination of a dog may show signs of anemia or fluid collection in the abdomen. Your vet will most likely perform routine lab tests and tests to look for abnormal clotting, and may aspirate fluid from the abdomen to see if there is blood. X-rays may be helpful in determining the extent of involvement, and ultrasound may be useful to determine heart and/or spleen involvement. Biopsies may be helpful and may provide a definitive diagnosis, but are also potentially dangerous as they may precipitate bleeding.

Treatment Guidelines

Note: Treatment of animals should only be performed by a licensed veterinarian. Veterinarians should consult the current literature and current pharmacological formularies before initiating any treatment protocol.

Treatment depends on the location of the tumor. Dermal tumors are most successfully treated as they often can be completely removed through surgery and treated with radiation therapy. Visceral involvement is much more difficult to treat and is rarely curative because of the high rate of metastasis. Surgery and chemotherapy are used but typically extend life only a few months at best.


Hemangiosarcoma. Modiano Lab at the University of Minnesota two bones

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Support Groups

This support group is for all types of canine cancer.

Yahoo Groups Canine Cancer

Hemangiosarcoma at Wikipedia two bones

Hemangiosarcoma at caninecancer.com one bone

Hemangiosarcoma at caninecancerawareness.org one bone

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