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Canine Hemangiosarcoma: Blood Vessel Cancer in Dogs

A common canine cancer, described
By Susan Tasaki, Content reviewed by Stephen Gardner DVM, DABVP, February 2021, Updated October 2021
Hemangiosarcoma in dogs

Hemangiosarcoma in dogs, one of the five most frequently diagnosed types, gives few warnings. Many of these fragile, blood-filled tumors aren’t discovered until they rupture, at which point, emergency surgery is the only treatment option.

What is it?

As its name suggests, these tumors develop from cells lining the blood vessels. Since the body is laced with blood vessels, a hemangiosarcoma can appear anywhere. That said, about 50 percent of the time, it affects the spleen, followed by the liver, heart or, rarely, the skin. This aggressive cancer (very similar to the relatively rare human angiosarcoma) most commonly afflicts middle-aged to older dogs, with a slight preference for males.

For the most part, what causes hemangiosarcoma in dogs to develop is unknown, although for those that develop on or under the skin, overexposure to sun on thinly haired regions like the belly, inner thighs and eyelids is thought to be a culprit.


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Signs and symptoms.

A tumor on or under the skin appears as a dark red/purple bump that may bruise or bleed, but early signs of internal tumors may be as subtle as lethargy and pale gums.

Initially, a hemangiosarcoma develops slowly. Then, as the tumor grows, blood vessels supporting it begin to leak, resulting in blood loss into the abdomen, and symptoms become more pronounced: weight loss, decreased appetite, increased panting, weakness, cough, a bulging belly.

The most common presentation seen by veterinarians in general practice is a dog who is suddenly weak, with a pendulous abdomen and pale oral membranes, the result of a mass on the spleen having ruptured and resulting in intra-abdominal hemorrhage (bleeding within the abdomen).

How is it diagnosed?

Hemangiosarcoma in dogs is diagnosed by reviewing suspicious skin masses (those larger than a pea and/or that have been around longer than a month), fine needle aspiration is used to secure a sample. But when an internal tumor is suspected, this method is much trickier. Instead, diagnosis usually involves bloodwork, an abdominal ultrasound, X-rays and a CT scan.

How is it treated?

Surgery and chemotherapy are the most common treatments, although a hemangiosarcoma is likely to have metastasized by the time it’s diagnosed. (A possible exception is a hemangiosarcoma in or under the skin, which is generally found sooner than one inside the body.) The principal goal of treatment is to slow down or delay the spread of the tumor and prevent life-threatening bleeding episodes. Currently, a cure, or even a remission, is extremely unlikely.

A spleen mass that ruptures requires surgery to remove the spleen. While the surgery can be life-saving, if the mass is a hemangiosarcoma, it will have already metastasized microscopically. Because approximately 50 percent of bleeding masses on the spleen may be benign, a splenectomy and pathologic evaluation of the spleen are worth pursuing, though it may only give the dog a few more months of quality life if the mass turns out to be a hemangiosarcoma. Within three to four months, the dog will have multiple tumors throughout the lungs and other parts of the body.

A 2012 study undertaken at the University of Pennsylvania reported success with an extract of a medicinal mushroom, Coriolus versicolor, in extending the lives of 15 Golden Retrievers with hemangiosarcoma. The mushroom contains a compound called polysaccharopeptide, or PSP, which some studies have suggested has both immune-boosting properties and a tumor-fighting effect. It has no side effects and is relatively inexpensive. (It’s been studied for use with human cancer patients as well, also with positive results.) However, to date—probably due to a lack of research—it’s rarely suggested or used by veterinary oncologists.

Researchers at the University of Minnesota College of Veterinary Medicine led by Jaime Modiano, VMD, PhD, are approaching the disease from a different direction. The Shine On project is following 209 otherwise healthy dogs who completed the third phase of the study in order to establish the reliability of the results of a novel blood test. Using this test, researchers assigned each dog a level of risk.

Currently, it’s estimated that a dog who tests negative for hemangiosarcoma has a less than 1 percent likelihood of developing it over a six-month period, while more than 90 percent of dogs with a positive test require further evaluation.

Dogs at high risk are eligible to receive eBAT, a genetically engineered drug developed at the university in 2017, as a preventive. According to the drug’s creator, Daniel A. Vallera, PhD, “eBAT was created to specifically target tumors while causing minimal damage to the immune system. … [It] was selected for this trial because it can simultaneously target the tumor and its vascular system.” In other words, it kills emerging cancer cells and inhibits the environment they need to grow.

Findings to date indicate that not only can the novel blood test accurately indicate the presence of hemangiosarcoma in otherwise healthy dogs with a 90 percent accuracy rate, it can also predict when treatment fails and the disease comes back.

Are certain breeds predisposed?

Golden Retrievers, German Shepherds, Portuguese Water Dogs, Boxers and Skye Terriers are the most commonly affected breeds by hemangiosarcoma cancer.

Susan Tasaki, a freelance editor and writer, lives in the San Francisco Bay Area with her Husky, who wishes they both got out more.