Hemangiosarcoma in Dogs

Hemangiosarcoma in Dogs: What Every Dog Owner Should Know I saw this almost every weekend in the ER. This is an important one!

Hemangiosarcoma is one of the cancers I worry about most in dogs because it can be silent, aggressive, and capable of causing life-threatening internal bleeding with very little warning.

Emergency warning signs: Collapse, pale gums, sudden weakness, a distended abdomen, or difficulty breathing may indicate internal bleeding or another life-threatening complication. Seek emergency veterinary care immediately if your dog develops any of these signs.

Hemangiosarcoma (HSA) develops from the cells that line blood vessels. It most commonly occurs in the spleen, heart, liver and skin, although it can develop in other organs as well. The visceral forms—particularly those involving the spleen, liver and heart—are much more aggressive than many other types of tumors. (Cornell Vet School)

What makes hemangiosarcoma so dangerous?

These tumors are often filled with blood and can rupture. A dog may appear completely normal and then suddenly become weak, pale, collapse, develop a distended abdomen, or have difficulty breathing because of internal bleeding.

Sometimes, however, the signs are much more subtle:

* Decreased energy

* Intermittent weakness

* Decreased appetite

* Weight loss

* Pale gums

* Exercise intolerance

* Episodes of collapse

Unfortunately, these signs can come and go, making the disease particularly difficult to recognize early. (Cornell Vet School)

How do we look for hemangiosarcoma?

When I am concerned about hemangiosarcoma, imaging is extremely important. However, no single test can reliably rule this cancer in or out.

Abdominal ultrasound

An abdominal ultrasound allows us to carefully examine the spleen, liver, kidneys, abdominal lymph nodes, and other abdominal structures.

We are looking for masses, nodules, abnormal organ architecture, free abdominal fluid, and evidence that disease may have spread.

Ultrasound is especially useful for evaluating a splenic mass and determining whether there are other suspicious lesions within the abdomen. (DOI)

It is important to understand, however, that an ultrasound can identify a mass but cannot definitively tell us what type of tumor it is. Ultimately, a diagnosis of hemangiosarcoma is generally confirmed through examination of tissue by a pathologist. (Cornell Vet School)

Thoracic radiographs

Chest X-rays are another important part of staging.

We look for evidence of disease involving the lungs and evaluate the chest for other abnormalities. Three-view thoracic radiographs are commonly recommended when staging dogs with suspected visceral hemangiosarcoma. (DOI)

One important point for owners to understand is that normal chest X-rays do not necessarily mean that cancer has not spread.

Hemangiosarcoma can spread microscopically before metastatic disease becomes visible on imaging. (Cornell Vet School)

Targeted ultrasound of the heart

I also think there is an important role for targeted ultrasound of the heart when hemangiosarcoma is suspected or when we are staging a patient with a concerning mass. This focused examination can detect minor to major bleeding around the heart, called pericardial effusion. We like to check for this because cardiac hemangiosarcoma masses can be difficult to identify unless fluid has accumulated within the pericardial space.

Hemangiosarcoma can occur in the heart, particularly around the right atrium/right auricle, and some cardiac tumors can be difficult or impossible to characterize adequately with chest radiographs alone.

An echocardiogram gives us a much closer look at the heart and can help determine whether there is a mass, abnormal fluid around the heart, or other cardiac abnormalities. (Cornell Vet School)

What happens if we find a splenic mass?

This is where things can become complicated.

Not every splenic mass is hemangiosarcoma. Some are benign, and others are different types of cancer. Unfortunately, imaging alone cannot always tell us which one we are dealing with.

If a splenic mass is large, cavitated, bleeding, or otherwise highly suspicious, surgical removal of the spleen (splenectomy) may be recommended. This both removes the source of potential life-threatening bleeding and allows the entire mass to be submitted for histopathology.

If the tumor is hemangiosarcoma, surgery is generally followed by a discussion about chemotherapy because of the high likelihood that microscopic disease is already present elsewhere in the body. (Cornell Vet School)

What about chemotherapy?

This is one area where veterinary medicine can be very different from human medicine.

When people hear the word chemotherapy, they often immediately think about the severe side effects that can occur during human cancer treatment.

Our goals in veterinary oncology are somewhat different.

For most dogs, our goal is not to push the body to its absolute limit in an attempt to cure the cancer at any cost. Our goal is generally to slow the progression of disease while maintaining an excellent quality of life.

Dogs also receive different doses and treatment schedules than people, and veterinary chemotherapy protocols are specifically designed with quality of life in mind. Many dogs tolerate chemotherapy surprisingly well. Some may experience temporary decreased appetite, vomiting, diarrhea, lethargy, or low white blood cell counts, but severe side effects requiring hospitalization are much less common than many owners expect. (PetMD)

For canine hemangiosarcoma, doxorubicin-based chemotherapy is one of the most commonly used approaches. Other drugs and combination protocols may also be considered depending on the individual patient, stage of disease, heart health, and goals of treatment. (Cornell Vet School)

Does chemotherapy cure hemangiosarcoma?

Unfortunately, usually not.

Hemangiosarcoma is extremely good at spreading before we can detect it. This is why a dog can have a splenic tumor removed and still eventually develop cancer elsewhere.

The purpose of chemotherapy after surgery is primarily to delay the development and progression of microscopic metastatic disease.

Studies have demonstrated longer survival in some dogs treated with surgery followed by doxorubicin compared with surgery alone. In one retrospective study of dogs with visceral hemangiosarcoma, median survival was 66 days with surgery alone versus 274 days with surgery followed by doxorubicin. Individual outcomes vary considerably, however, and these numbers should never be interpreted as a prediction for a particular dog. (PubMed)

What if the tumor is in the heart?

Cardiac hemangiosarcoma can be particularly challenging because complete surgical removal is usually not possible.

Depending on the location and extent of disease, treatment may involve chemotherapy and, in selected cases, surgery or other supportive procedures. An echocardiogram can be extremely helpful in determining what we are dealing with and what treatment options might realistically be available. (Cornell Vet School)

So, should we screen every dog for hemangiosarcoma?

This is an important question, particularly for older dogs and breeds that are predisposed to the disease.

There is no perfect screening test that can guarantee that a dog does not have hemangiosarcoma. However, in an older or higher-risk dog—especially one with concerning clinical signs—routine physical examinations, bloodwork, and appropriate imaging can sometimes identify problems before a catastrophic bleeding event occurs.

And when a concerning abdominal mass is discovered, I think it is important to look beyond just the mass itself.

Abdominal ultrasound + thoracic radiographs + targeted cardiac ultrasound when indicated can provide a much more complete picture of what may be happening.

The bottom line

Hemangiosarcoma is a devastating disease, but finding it does not necessarily mean that there is nothing we can do.

Our job is to determine:

Where is the tumor?

Has it spread?

Is the patient bleeding?

Can the tumor be surgically removed?

Would chemotherapy be appropriate?

And most importantly—what treatment will give this individual dog the best quality of life for as long as possible?

Early investigation of suspicious signs and appropriate staging can help us answer those questions and make an informed treatment plan.

As veterinarians, we cannot always prevent hemangiosarcoma. But we can work to recognize it, stage it, treat it when appropriate, and help families make the best decisions possible for their individual pet.

Dr. Cassie Floral city Animal clinic, Inverness Fl ©Copyrights 2026