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FAQ: What Are the Early Signs of Hemangiosarcoma in Dogs?

Updated: Nov 5, 2023



Hemangiosarcoma is one of the most devastating canine cancers. It seems as if it comes on fast, it's very malignant, and it's subtle until it reaches a point where it's too progressed to ignore – and at that point, it's difficult to treat. Because of this combination of factors, it's critical to perform screenings and watch for even the most subtle signs of the cancer to catch it as early as possible.


What is Hemangiosarcoma?


Hemangiosarcoma is relatively unique among cancers as a cancer that primarily affects dogs. Many other kinds of cancer are found in both people and dogs or across other species, but hemangiosarcoma is almost exclusively canine.



Specifically, hemangiosarcoma is a sarcoma, which is a family of cancers that arise as an uncontrolled growth of connective tissues, bone, fat, and muscle. In this case, the cancer is a sarcoma of the vascular endothelial cells – blood vessel lining. Because blood vessels can occur anywhere in the body, so too can hemangiosarcoma; however, it's more common in areas with dense clusters of blood vessels. In dogs, that means it occurs most frequently in the spleen, liver, heart, and skin.


"Hemangiosarcoma is relatively common in dogs; it is estimated that this type of cancer accounts for 5-7% of all tumors seen in dogs. Considering the lifetime risk of cancer for dogs is between 1 in 2 and 1 in 3, we can calculate that 1.5 to 2.5 million of the ~72 million pet dogs in the United States today will get hemangiosarcoma and succumb from it." – American Kennel Club.

Hemangiosarcoma can be considered cutaneous (on the skin) or non-cutaneous (not skin-related). There are no known direct links or causes of hemangiosarcoma; while sunlight exposure can cause it on dogs with thin fur in areas like their bellies and eyelids, non-cutaneous hemangiosarcoma is a mystery.


Are Some Breeds Predisposed to Hemangiosarcoma?


Hemangiosarcoma in dogs can occur at any age and in any breed. However, it occurs more frequently in dogs over the age of six. Some breeds are also more susceptible to non-cutaneous hemangiosarcomas: Golden Retrievers, German Shepherds, Portuguese Water Dogs, Bernese Mountain Dogs, Flat Coated Retrievers, Boxers, and Skye Terriers, among others.



Golden retrievers, as a very common and popular breed, account for a large proportion of hemangiosarcoma cases, and thus, much of the literature surrounding the cancer focuses on that breed.


What Are the Early Warning Signs of Hemangiosarcoma?


Part of the danger of hemangiosarcoma is that there is very little in the way of early symptoms.


Hemangiosarcoma is a complex disease. In some cases, it manifests as an "indolent" condition. Medically speaking, this means it progresses slowly and may not cause pain or noticeable changes in behavior until it's quite advanced, potentially having metastasized throughout the body. This nature can sometimes give a false sense of security, as clients or patients might not detect symptoms until the cancer is at a critical stage. However, it's crucial to understand that hemangiosarcoma doesn't always follow this pattern. There are instances where it can arise seemingly overnight, rapidly developing into a sizable tumor within just a few days. Both scenarios are possible, highlighting the unpredictable and aggressive nature of this cancer.

"Dogs harboring even large hemangiosarcomas may show no clinical signs or evidence that they have a life-threatening disease." – American Kennel Club.

Some clients report minor symptoms in their dogs, including lethargy, weakness, decreased interest in normal activities, and decreased appetite, usually a relatively short time before diagnosis.



Later signs include collapse, a distended abdomen, severe respiratory distress, pale gums, and severe internal bleeding when a tumor ruptures.


"Superficial skin tumors typically appear as a red to purple colored region of skin or bump that may bruise or bleed spontaneously. When tumors occur under the skin, a soft or firm swelling may be palpable. However, it is impossible to tell from appearance or feel whether a skin mass is benign or malignant." – North Carolina State Veterinary Hospital.

Indeed, often, the first sign of hemangiosarcoma is a sudden collapse and a diagnosis of severe internal bleeding caused by a ruptured tumor. Hemangiosarcoma is a cancer of the blood vessel lining; the cells replicate out of control but still try to do what they're supposed to do, creating twisted and malformed masses of blood-carrying vessels that can clot, swell, or otherwise cause problems, leading to ruptures.


"Generally, the tumor cells retain some normal aspects of behavior, so they try to make blood vessels. But these vessels are tortuous and malformed, and blood cells tend to pool in them and clot. The clots then prevent blood and nutrients from reaching tumor cells, in turn causing them to die. This creates small ruptures in the tumor through which blood may escape into the abdomen, heart sac, chest, or subcutaneous space. Depending on the amount of blood lost, affected dogs may show non-specific (constitutional) signs such as lethargy and weakness, but these are transient and resolve as dogs reabsorb the blood components and make new blood cells. The clinical signs are recurrent, but they also are subtle enough to go unnoticed for some time." – American Kennel Club.

This is, again, part of what makes hemangiosarcoma such a difficult disease. While it doesn't grow or spread rapidly, it often feels like it comes out of nowhere because it showed no symptoms until it was much more advanced than most cancers get before being discovered.


How is Hemangiosarcoma Diagnosed?


When diagnosing cancers, two methods are generally used: fine-needle aspiration and biopsy. Fine-needle aspiration uses a small needle to extract cells from a tumor, which can be examined under a microscope. However, because of the nature of hemangiosarcoma, this procedure is rarely effective. This is because hemangiosarcomas are not solid; they're fragile and prone to bleeding, so it's much more difficult to collect cells from the tumor itself.


"Tumor cytology can also be performed, being less invasive compared to biopsy, but the diagnosis will not always be reached because of low cellular exfoliation and high hemodilution." - NCBI.

In other words, it's hard to get actual cells of the tumor, and the cells you do get will be washed out with blood and harder to identify.



A biopsy is a similar procedure, except it takes more of the tumor and uses different forms of inspection to identify it. The drawback to this is that certain tumor locations, particularly the heart, are difficult or impossible to safely biopsy. Imaging and other examinations can be used to check for heart masses.


What Are the Treatment Options for Hemangiosarcoma?


Treatment options vary depending on the location and staging of the cancer when it is discovered.


For cases where the tumor is isolated and solitary – meaning there's only one, and the cancer has not spread to other parts of the body – surgery can be a viable treatment option. The tumor, when accessible, can be removed, along with a healthy margin around it, to ensure complete extraction. A notable example is when hemangiosarcoma appears in the spleen. In many instances, it's confined just to the spleen, and surgical removal of the spleen is relatively straightforward. However, due to the origin of the cancer, there are times when it manifests in locations where surgical removal is more challenging, such as the heart. And, because of its indolent nature, there are instances when it isn't diagnosed until it has spread.


The second treatment option currently available is chemotherapy. One of the commonly used drugs for this purpose is doxorubicin, which is administered via IV. Chemotherapy aims to slow, stop, or potentially even reverse tumor growth. Because tumors grow rapidly and voraciously, targeting their unchecked growth can effectively hinder them. Chemotherapy can be an interim solution to slow the disease's spread while considering other treatment avenues, or it can be employed to extend the life of the dog.


Finally, radiation therapy is sometimes an option for cutaneous and subcutaneous hemangiosarcomas. Radiation can be used around the edges of a tumor that cannot be fully excised with surgery to help kill off any remaining cancerous cells, or it can be used to reach tumors that are otherwise difficult or impossible to treat surgically.

"The news is not all bad. We have identified some of the fundamental properties of canine hemangiosarcoma, and it is possible one or more of these may prove to be an "Achilles heel" for the tumor. For example, most of these tumors make growth factors that they need to survive, or they "coerce" cells in their environment to do this for them. One of these growth factors is vascular endothelial growth factor-A or VEGF, which acts by binding specific receptors on the hemangiosarcoma cells. New drugs under development by various pharmaceutical companies are designed specifically to interfere with the signals transmitted by these receptors. The reliance of hemangiosarcoma cells on VEGF signals to survive should make them more sensitive than normal cells to these drugs. Several groups are working to bring these drugs into the clinic, but the process is slow because testing must be done in a careful, deliberate way to ensure the compounds are safe and effective." – American Kennel Club.

So, while newer, potentially more effective treatments may be on the horizon, the current options are limited. For conditions like hemangiosarcoma, there is the Torigen vaccine and the possibility of targeted therapy through a genetic analysis by FidoCure or Vidium. As for the EGFR vaccine, it's true that it's not yet widely available. If you're seeking the most cutting-edge treatments, there might be clinical trials in your area that you can consider enrolling your clients and patients in. However, the availability of these trials heavily depends on location, so it's challenging to provide a definitive answer.


Do the Treatments for Hemangiosarcoma Have Side Effects?


Each potential treatment has its own array of potential side effects.


Surgery, of course, is well understood. Any surgery has risks, and the larger the surgery, the more dangerous it can be. When you're working with organs and visceral flesh, it can be a lengthy recovery and a dangerous surgery even before the kind of cancer hemangiosarcoma is.


Radiation is somewhat lighter. Radiation can be targeted to primarily affect the tumors and will have less impact on surrounding tissues; however, it can still cause irritation of the skin and ulceration. These side effects generally heal over time but can be noteworthy.



Chemotherapy, meanwhile, is largely free from side effects, barring outside circumstances. Chemotherapy gets a bad rap because it's very harsh in humans, but dogs are much more resilient to it. This is partially due to species reactions but also due to goals: in humans, chemo is rougher and more intense because it's meant to be curative. In dogs and other pets, quality of life is prized over the length of life, so chemo with reduced side effects, balanced to keep the pet happy for as long as it's viable, is a more sought-after goal.


With canine chemo, most side effects end up revolving around gastrointestinal distress, lack of appetite, and nausea. Part of a good chemotherapy regimen is a set of drugs to offset the side effects; many dogs on chemo display nearly no side effects from the medications themselves.


What is the Prognosis for Dogs with Hemangiosarcoma?


Unfortunately, due to the frequently late diagnosis and the nature of the cancer, the prognosis for hemangiosarcoma is generally grim.


"Average survival time with surgery alone is one to three months. The 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." – Morris Animal Foundation.

Fortunately, progress is slowly being made in three areas.



1. Ongoing development of potential early detection tests may make it more realistic to detect and treat hemangiosarcoma before it reaches a crisis point.


2. The development of novel drugs may provide new avenues for more effective and isolated (rather than systemic) treatment of hemangiosarcoma specifically.


3. Further study of the disease may uncover previously unidentified links to causative factors that can be adjusted to minimize the incidence of hemangiosarcoma.

Unfortunately, as it currently stands, none of these have reached fruition yet.


Helping You Help Your Clients


Hemangiosarcoma is a devastating disease because, due to its hidden growth, by the time it's detected, the patient has very little time left. As a vet, you want to provide the best possible outcomes for your patients and for your clients alike. Hemangiosarcoma is a tricky disease, so it stands to reason that you may want to consult a second opinion for the correct course of action.



That's where we come in. Oncology, along with several other kinds of veterinary medicine, is within our set of specialties; we can provide a second opinion and a report like this to help you work with your clients to make the best possible decisions. If you're interested in our consulting, we encourage you to reach out.

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