Hemangiosarcoma in Dogs: cancer of the blood vessels

What is hemangiosarcoma? 

One of the most challenging diseases in dogs is hemangiosarcoma. It is not only challenging but also quite mysterious according to the vets. The hemangiosarcoma spreads rapidly and strikes quickly. It is a tumour of the cells lining the blood vessels and it is incurable. It also occurs almost exclusively in dogs. Dogs around 6 years or older are most susceptible. Breeds such as Golden Retrievers, German Shepherds, Boxers are usually the most common ones afflicted by hemangiosarcoma.

In most cases, hemangiosarcoma affects the spleen and the heart of these breeds. Around 25% of the dogs that develop hemangiosarcoma in the spleen also develop a tumour in the heart. There have been cases where the skin is affected but barely noticed until such time that a tumour ruptures and causes hemorrhage; although the metastasis occurs very early in the disease. 

Hemangiosarcoma is most likely in areas that have a rich blood supply. It may start with an increased growth of cells that line the blood vessels; but, since the spleen and the heart are the two organs that have a large supply of blood,  hemangiosarcoma strikes these two organs usually.

Some dogs may show signs of lethargy or anorexia merely as episodes that recur. But, unfortunately in most cases, these dogs afflicted by hemangiosarcoma tend to collapse, or have an abnormally increased heart rate or respiratory difficulties. They also develop pale mucous membranes when there is a hemorrhage due to a ruptured tumour.

Causes of hemangiosarcoma in dogs

Identifying the cause of hemangiosarcoma has been found highly challenging. At best, it has been seen as a combination of environment and some genetic condition. But, this is yet to be proven. In the case of hemangiosarcoma in the skin, the conclusion is that it is caused by too much sunlight as it is found to be a contributing factor. 

Symptoms of hemangiosarcoma in dogs

Since the hemangiosarcoma can rupture quite suddenly and lead to excessive blood loss, it may be too late to remember any symptoms that you may have noticed.  It may also be too late to realize that there has been internal bleeding. Some of the symptoms that can be seen include: fatigue, anorexia, excessive panting not related to exercise, colour of the gums and tongue becoming pale, a weak pulse, and a sudden collapse. 

Time is of the essence in each of the symptoms.  Each one of them can be considered a medical emergency in the case of hemangiosarcoma. Even if a tumour is detected immediately and surgically removed, chances of survival remain bleak.

Diagnosis of hemangiosarcoma in dogs

Your dog’s vet may try the physical examination first by trying to palpate the enlarged spleen. This is not always easy because of a blood-filled abdomen. You may need to submit your dog to blood work to check for anemia, low platelet count, or blood coagulation. An intravascular coagulation is when several blood clots occur and they block the blood vessels. X-rays and ultrasound may also be required to look for an enlarged spleen showing many nodules, masses in the abdominal area or the heart.

Your dog’s vet may also tap the abdominal cavity with a needle as in performing an abdominocentesis. Studying the cytology through this may help in identifying hemangiosarcoma; however, it is considered a risky procedure because it may cause bleeding. There are only two options if this risky procedure were to be undertaken – emergency surgery to stop the bleeding or euthanizing the dog. 


The importance of regular visits to your dog’s vet cannot be overstated. However, at best any and all of the tests including blood work and ultrasound may only be able to look for symptoms before hemangiosarcoma occurs. These are not necessarily fool proof, similar symptoms may be seen due to a variety of factors including other diseases.

If the hemangiosarcoma is of the spleen, survival time may be a maximum of three months. If the hemangiosarcoma is in the heart, survival time may be a maximum of five months. Chemotherapy may help by extending this survival time by a few days. 

Some of the new therapies that are becoming popular include immunotherapy, using antimetastatic agents, and even mushroom extracts in a few cases to increase the survival time. 

What can you do as a pet parent?

Watch for signs in your dog’s mucous membranes. Pay attention to them by studying the colour of the gums by lifting the upper lip. Understand the area under normal conditions; for example, your dog may have some pigmentation in the gums. Examine the area with a strong light and look for a difference between the normal pigmentation and the pink areas on your dog’s gums. Your dog’s survival depends on prompt diagnosis and action. Simply understanding the disease may help you spot a potential problem and take quick action.

As a pet parent, hemangiosarcoma can be heartbreaking. All you can do is provide as much supportive care as your dog needs and be fully present. Try and store up memories and mentally prepare yourself for the final outcome. Let your dog know he is loved!


The information contained in VOSD Vet Advice™ is not intended nor implied to be a substitute for professional medical action which is provided by your vet. You assume full responsibility for how you choose to use this information. For any emergency situation related to a dog’s health, please visit the nearest veterinary clinic.

Do you find this information useful? For more medical advice, visit the VOSD website.