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Updated October 26, 2023 – Hemangiosarcoma is a common and deadly cancer of dogs. The cancer tends to grow and spread rapidly, rarely giving the owner any clue their dog is harboring a deadly disease – until it suddenly strikes. On average, a beloved dog succumbs to hemangiosarcoma every two minutes.

Knowing more about how this cancer develops and learning to recognize the subtle signs of the disease are important for owners, not only to spot a potential problem, but also to know the facts if hemangiosarcoma affects their dog. Check out our hemangiosarcoma resources page to learn more about what the Foundation is doing to address this devastating disease and how you can help!

Hemangiosarcomas often are found in sites with a rich blood supply

There is growing evidence that hemangiosarcoma cancer cells originate in the bone marrow but rapidly spread to other locations in the body. Hemangiosarcoma often is detected first in the heart and spleen, the two most common sites where this type of tumor is found. This predilection for the heart and spleen is the reason these tumors are so deadly. Hemangiosarcomas can suddenly rupture, causing massive blood loss, and forcing owners and veterinarians to make difficult decisions within minutes of diagnosis.

Hemangiosarcoma is a disease of larger-breed, older dogs

Hemangiosarcoma most commonly affects:

  • Middle-aged to older dogs
  • German shepherds, golden retrievers, Portuguese water dogs and Labrador retrievers
  • Slightly more males than females (in some studies)

Unfortunately, no clinical signs (symptoms) are classic for hemangiosarcoma other than sudden, profound, internal bleeding. Other clinical signs reported by owners include:

  • Intermittent lethargy or fatigue
  • Anorexia
  • Panting
  • Sudden collapse
  • Sudden death

Most pet owners are quick to act in cases of sudden collapse and time is of the essence in cases of hemangiosarcoma. These are true medical emergencies and many patients require immediate surgery to remove the bleeding mass (if possible), followed by supportive care to survive.

Long-term survival statistics are bleak

Even when a tumor is quickly detected and removed, the outlook for dogs with hemangiosarcoma is grim. Statistics show that:

  • Average survival time with surgery alone is one to three months
  • Average survival time with surgery and chemotherapy is five to seven months
  • 90% of dogs are deceased one year post-diagnosis despite surgery and chemotherapy with almost 100% mortality two years post-diagnosis

Survival times have remained static for nearly 30 years, and new treatments are desperately needed. This is where Morris Animal Foundation comes in.

New ideas and research on an old foe

Many current and past studies have been devoted to learning more about this terrible cancer. New findings reported in the last two years include:

  • A recent study focused on small dogs with hemangiosarcoma found similar survival statistics as large-breed dogs with hemangiosarcoma
  • Work continues on the effect of spay/neuter on the incidence of hemangiosarcoma, but no definitive conclusion has been reached yet
  • Researchers from North Carolina State University found a higher incidence of the bacteria Bartonella spp. in some dogs with hemangiosarcoma and are doing more studies to clarify their findings

Results from the Golden Retriever Lifetime Study will be invaluable as we try to answer these important questions.

Golden Retriever Lifetime Study

Hemangiosarcoma is an important cancer of golden retrievers and is one of several cancers of special interest to the Foundation’s Golden Retriever Lifetime Study. Currently, hemangiosarcoma is the leading cause of cancer death in our cohort of 3,044 dogs. We’re monitoring and collecting extra tissue and other biological samples from all dogs in our cohort diagnosed with hemangiosarcoma.

In addition to samples collected at the time of diagnosis or death, we have banked samples on affected dogs dating back years that may point to risk factors associated with this cancer. Our hope is that researchers will be able to use these samples to develop early diagnostic tests as well as understand possible genetic links to this deadly disease. Our team is working to promote Study data and samples to researchers from around the world, and inviting them to submit proposals to learn more about hemangiosarcoma and other cancers in golden retrievers.

The Golden Oldies project, which will compare DNA from older golden retrievers without cancer to DNA from Study dogs with cancer (including hemangiosarcoma), will provide additional, critically needed data on the underlying genetics of this cancer. Findings from this project could ultimately result in a diagnostic test to identify dogs at risk for this cancer.

We’re trying to improve the odds for dogs with hemangiosarcoma

Morris Animal Foundation has invested more than $3 million in 20+ years of research to improve the quality and duration of life for dogs diagnosed with hemangiosarcoma.

Our funded research has focused on:

  • Disease basics – understanding the basic biology of hemangiosarcoma may open the door to new diagnostics, treatments and prevention
  • Overcoming chemotherapy resistance – understanding why hemangiosarcoma becomes drug resistant could improve treatment success as well as identify new chemotherapeutic agents
  • Genetic links – studying breeds commonly affected by hemangiosarcoma could lead to new diagnostic testing and clues to the role genetics play in the development of this disease

You can find more information in our Hemangiosarcoma White Paper and our upcoming Hemangiosarcoma Initiative.

Help Animals Today

Morris Animal Foundation has been a leader in canine cancer research, including hemangiosarcoma, since 1962. We need your help to keep the momentum and find better ways to diagnose, treat and maybe cure cancer in animals. Learn more about ways you can help ensure that dogs everywhere live healthier, happier and longer lives.


Hemangiosarcoma Initiative

Episode 52: New Ideas on Hemangiosarcoma in Dogs

Exploring the Link Between Hemangiosarcoma Subtypes and a Common Heart Drug

Hemangiosarcoma White Paper

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