Hemangiosarcoma in dogs is an aggressive, malignant tumor of blood vessel cells. With the exception of the skin form of hemangiosarcoma, a diagnosis of hemangiosarcoma is serious. Because these tumors start in blood vessels, they are frequently filled with blood and when a blood-filled tumor ruptures, it can cause problems with internal or external bleeding.

Hemangiosarcoma can theoretically arise from any tissue where there are blood vessels, which are essentially anywhere in the body, but usually appear in the skin, soft tissue, spleen, or liver with the most common site being the spleen. They are highly metastatic and will frequently spread to the brain, but also to the lungs, spleen, heart, kidneys, skeletal muscle, and bone. This type of cancer in dogs is typically classified as dermal, subcutaneous or hypodermal, and visceral.

Dermal Hemangiosarcoma

The skin form of hemangiosarcoma is the most easily removed surgically and has the greatest potential for complete cure. The skin form looks like a rosy red or even black growth on the skin. This form is associated with sun exposure and thus tends to form on non-haired or sparsely-haired skin (such as on the abdomen) or on areas with white fur. Dogs with short white haired fur (such as Dalmatians and pit bull terriers) are predisposed to the development of this tumor. Approximately 1/3 of cases will spread internally in a malignant way usually associated with cancer so it is important to remove such growths promptly. This form of angiosarcoma is covered more broadly in the Skin Cancer section of this website.

Subcutaneous (hypodermal) Hemangiosarcoma

The overlying skin of a subcutaneous hemangiosarcoma is often completely normal. However, below the skin is a dark red blood growth. Up to 60% of hypodermal hemangiosarcomas spread internally

Visceral Hemangiosarcoma – spleen

Visceral Hemangiosarcoma - Spleen

The spleen is a large abdominal organ which while not essential for life, serves an important role in blood and lymph functions. Splenic growths have the unfortunate tendency to break open and bleed profusely regardless of whether they are benign or malignant. While a splenectomy (removal of the spleen) ends the prospect of this type of life-threatening sudden bleed, splenic hemangiosarcoma is still a rapidly spreading malignancy.

When a splenic mass is detected, it may not be possible to tell prior to splenectomy whether or not the mass is malignant or not although testing will most likely be performed to attempt to determine this. It has been estimated that 25% of dogs with splenic Hemangiosarcoma also have a heart-based Hemangiosarcoma.

Visceral Hemangiosarcoma – Heart

Visceral Hemangiosarcoma – Heart

Similar to splenic hemangiosarcoma, heart-based hemangiosarcoma tends to be life-threatening from the effects of bleeding. The heart is enclosed in a sac called the “pericardium.” When the hemangiosarcoma bleeds, the blood fills up the pericardium until it is so full that the heart inside is under so much pressure that it has no room to fill with the blood it has to pump. This is called pericardial effusion and must be treated before an emergent situation occurs.


Hemangiosarcoma Causes

The dermal form of Hemangiosarcoma in dogs is associated with sun exposure. It is uncertain what the causes are for the other forms of this disease, 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 less research has been done, and the amount of information about the cause of this tumor is somewhat limited.

Risk Factors

Hemangiosarcoma Risk Factors

Hemangiosarcoma Risk Factors

Hemangiosarcoma is more common in dogs than in any other species. It usually occurs in middle-aged to older dogs 6 to 13 years of age, although it has been seen in dogs less than one year of age. It tends to develop in mid to large size breeds and especially German shepherds, golden retrievers, labrador retrievers, Boxers, Dobermans, and English setters.

The most common primary location of this cancer in dogs is the spleen. Other primary locations include the heart, liver, skin, and bone; however, it can start in any location where blood vessels are present. These tumors usually spread to the lungs, liver, spleen, and heart.


Hemangiosarcoma Symptoms

Because hemangiosarcoma tumors most often develop in internal organs, frequently, there are few or no obvious symptoms before the onset of severe clinical signs of disease. Signs of this disease are usually the result of the tumor rupturing, which causes bleeding. This may occur without any warning, and the symptoms will depend upon where the tumor is located. The most common symptom will be a lump under the skin, visible bleeding, sometimes in the form of nosebleeds, tiring easily, episodes of unexplained weakness, pale color in the gums, difficulty breathing, abdominal swelling, seizures, abnormal heart rhythms, collapse, and depression.

When the tumor is located in the spleen or liver, the clinical signs are usually due to rupture of the tumor and subsequent bleeding into the abdomen. This causes anemia, weakness and if the bleeding is severe, collapse. The gums may appear to be pale or white. In relatively few dogs, the diagnosis is made before the tumor ruptures.

When the tumor is located in the heart, it can cause symptoms, such as weakness, collapse, difficulty breathing, exercise intolerance, and fluid build-up in the abdomen. This is usually due to the development of fluid around the heart, called pericardial effusion. The pericardium is a thin sack that surrounds the heart and with hemangiosarcoma, the pericardium fills up with blood due to rupture of the tumor.

When the tumor occurs in the skin, a mass or lump can usually be felt in or under the skin. The mass may become ulcerated and bleed. When the tumor occurs in a bone, it can cause pain and discomfort. In some locations, such as a rib, the tumor can be felt as a firm swelling in the bone.


Hemangiosarcoma Diagnosis

In order to diagnose the potential disease, the veterinarian will begin with an examination of the dog. This 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 radiographs (x-rays) of the chest and abdomen to determine the extent of organ involvement and whether metastasis is present. Definitive diagnosis is accomplished by biopsy or removal of the tumor. This can be challenging because there may be multiple tumors and/or the primary tumor site may be difficult to determine. There is also a significant risk of severe hemorrhage during these surgical procedures.


The treatment for hemangiosarcoma depends upon the location of the tumor. Treatment is more successful when this cancer occurs on the skin than when it is found in an internal organ. Most dermal hemangiosarcomas can be successfully treated and cured by surgical removal of the tumor. Chemotherapy is often used in addition to surgical excision if the veterinarian was not able to remove the entire tumor or it has penetrated into the subcutaneous tissue or muscles below the skin. Radiation therapy is also used to treat dermal hemangiosarcoma.

The visceral forms of this disease require more aggressive treatment, and even then, the treatment will not likely be curative. If a tumor is identified when it is small, it may be possible to remove the spleen if the tumor is there or to remove tumors found near the heart and prolong the dog’s life. A pericardial tap may be required to treat the build-up of fluid around the heart or the pericardial sac may be removed. Surgery alone will not make much difference because these are highly malignant tumors and most have spread by the time they have been diagnosed. For this reason, combining surgery with chemotherapy is the standard treatment. Many chemotherapy protocols exist which may include the following drugs: cyclophosphamide, vincristine, doxorubicin, and Cytoxan. The use of radiation has not been proven to be useful in fighting this disease at this time.

Treatment for bleeding disorders and aggressive supportive care also prolong the life of patients with hemangiosarcoma.


Hemangiosarcoma is rarely curable and the long-term prognosis for dogs with hemangiosarcoma is poor. Dogs with internal organ involvement who are treated with surgery alone live an average of only 2 months. Dogs who do not have identifiable metastasis at the time of surgery and who are treated with chemotherapy live a median of 6 to 10 months. Some dogs with demonstrable metastasis may also respond to chemotherapy, providing a prolonged quality of life compared with dogs that are not treated at all. Dogs with this type of cancer located in the subcutaneous tissues (just under the skin) live a median of about 6 months with surgery alone.

Studies have shown that surgery to remove the spleen (splenectomy), offers a median survival time of 19-83 days. Dogs with a primary tumor of the spleen that has not ruptured have a better prognosis. However, if the spleen has ruptured before it can be removed, the prognosis is poorer. The combination of splenectomy and chemotherapy can increase survival time but fewer than 10% of dogs survive more than one year.

The blood disorder that most commonly accompanies the presence of hemangiosarcoma tumors is disseminated intravascular coagulation (DIC). This is blood clotting that is occurring inappropriately inside the blood vessels. It uses up all of the blood clotting elements rapidly and dogs with this condition usually have platelet deficiencies, increased blood clotting times, a decrease in fibrin content in the blood, and an increase in fibrin degradation products (FDPs). This may be the cause of death in many dogs affected by hemangiosarcoma.

Read Ginger’s amazing story of hemangiosarcoma

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earn About the Dog Cancer Diet That Defied the Odds and Restored Henry Back to Health! Sadly, cancer in dogs is on the rise. I first became aware of the dog cancer epidemic when my dog Henry was diagnosed with a malignant form of Hemangiosarcoma (an aggressive form of dog cancer).In bad shape and given six to eight weeks to live max, things didn’t look too good for us. The conventional approach of multiple surgeries and weekly chemo treatments seemed to be futile and beyond my financial means. Instead, I developed a holistic canine cancer diet that restored Henry back to health. Click here, it’s FREE!