Mar Vista Animal Medical Center

3850 Grand View Blvd.
Los Angeles, CA 90066




Hemangiosarcoma is a malignant tumor of blood vessel cells. With the exception of the skin form (which can often be eliminated by surgery), a diagnosis of hemangiosarcoma is bad news. This tumor is associated with serious internal bleeding and rapid internal spread. Fortunately, it is not a completely without therapy options and, as long as expectations are realistic, temporary remissions are possible.

Any breed of dog can be affected but a predisposition has been identified in the German shepherd dog, the golden retriever, and the Labrador retriever. Median age at the time of diagnosis is 10 years.

German Shepherd

German Shepherd

Golden Retriever

Golden Retriever

Labrador Retriever

Labrador Retriever

(Photocredit all three dogs:

Hemangiosarcoma can theoretically arise from any tissue where there are blood vessels (which amounts to anywhere in the body) but there are three classical locations which account for most presentations:

  • Skin and Subcutaneous forms
  • Splenic forms
  • Heart Base forms



The skin form of hemangiosarcoma is the best type to have as it is the most easily removed surgically and thus has the greatest potential for complete cure.

The skin forms of hemangiosarcoma are classified as either dermal and subcutaneous (also called hypodermal.) The true skin form looks like a rosy red or even black growth on the skin. This form is associated with sun exposure and thus tends to form on non-haired or sparsely haired skin, such as on the abdomen, or on areas with white fur. Dogs with short white haired fur (such as Dalmatians and pit bull terriers) are predisposed to the development of this tumor. Approximately 1/3 of cases will spread internally in the malignant way we usually associate with cancer so it is important to remove such growths promptly.

skin form of hemangiosarcoma

(Photo Credit: Joel Mills via Wikimedia Commons)



The biopsy report will indicate whether or not the growth was completely excised. If the tissue completely surrounding the growth is normal, this indicates that the growth has been removed completely and that it should not grow back.

If one wants to be absolutely positive that no tumor spread has yet occurred, the following non-invasive (but not inexpensive) testing is necessary.

  • Chest radiographs - hemangiosarcoma tends to spread to the lungs. Advanced tumor spread can be picked up with this simple test. (Spots of tumor spread must be 3 mm in diameter to be large enough to be visible on a radiograph.)
  • Ultrasound of the belly - specifically the spleen. Even a small splenic hemangiosarcoma should be detectable with ultrasound.
  • Ultrasound of the heart - even a small heart-based hemangiosarcoma should be detectable with ultrasound.



The overlying skin is often totally normal on top of a subcutaneous hemangiosarcoma and often the surgeon is surprised to find a dark red blood growth under the skin when the tumor is removed.

Since up to 60% of hypodermal hemangiosarcomas spread internally the above three tests to rule out tumor spread are more important.

  • If no sign of tumor spread is found after chest radiographs have been taken and ultrasound of the heart and belly are clear, prognosis is substantially better than if secondary tumor is found; however, additional treatment with chemotherapy is recommended if cure is the goal.
  • Surgery alone has been associated with a 172-day (approximately 6 months) median survival time.




(original graphic by

Radiograph of a dog's abdomen showing a dramatically enlarged spleen. The spleen has been outlined for those unfamiliar with reading radiographs. 

The spleen is a fairly deep-seated abdominal organ that tends to go unnoticed unless it develops a growth of unusual enlargement. Splenic growths have the unfortunate tendency to break open and bleed profusely regardless of whether they are benign or malignant. While a splenectomy (removal of the spleen) certainly ends the prospect of this type of life-threatening sudden bleed, splenic hemangiosarcoma is still a rapidly spreading malignancy.

When a splenic mass is detected, it may not be possible to tell prior to splenectomy whether or not the mass is malignant or not (though certainly basic testing is performed in an attempt to determine this.) Read about splenectomy to review the details of splenic mass evaluation. Chemotherapy after removal of the splenic hemangiosarcoma is reviewed here so see the hemangiosarcoma link on the splenectomy page when you are ready to return for more information.

  • 25% of dogs with splenic hemangiosarcoma also have a heart-based hemangiosarcoma. This generally is not representative of tumor spread but actually represents simultaneous development of the tumor in multiple sites. This is called "synchronous disease."
  • Survival time with surgery alone is 19 to 65 days for splenic hemangiosarcoma.



Like the splenic hemangiosarcoma, the heart-based hemangiosarcoma tends to exert its life-threatening effects by bleeding. Tumors are generally located around the right side of the heart base.

The heart is enclosed in a sac called the pericardium. When the hemangiosarcoma bleeds, the blood fills up the pericardium until it is so full that the heart inside is under so much pressure that it has no room to fill with the blood it has to pump.

On chest radiographs the heart is globoid (spherical). In fact, the actual heart is of normal shape but all that can be seen on the radiograph is the large round heart shadow of the pericardium filled to capacity with blood. Ultrasound is needed to truly see the effusion.

This condition, if allowed to progress, results in an emergency circulating collapse called a "pericardial tamponade" and can only be relieved by tapping the pericardium with a needle and withdrawing the excess fluid.

  • 63% of heart-based hemangiosarcomas have evidence of tumor spread at the time of their discovery.
  • Survival time for surgery alone (removing the pericardium and snipping off the heart-based hemangiosarcoma) is approximately 1-3 months. In a study presented in the Journal of the American Veterinary Medical Association in February 2005, 23 dogs with this type of tumor were studied. Of the dogs that had surgery, approximately half of them had some sort of post-operative complication, though most complications were minor and 87% survived and were released to go home from the hospital. Median survival time for dogs that had surgery without chemotherapy was 43-118 days (depending if the tumor was in the right atrium or just in the auricle, which is the small ear-like area adjacent to the atrium).
  • Eight of the dogs that survived surgery went on to receive chemotherapy in addition to surgery and these individuals had much longer survival times (median survival of 175 days vs. 42 days for dogs who had surgery without chemotherapy).

The dark red jelly-like material is the tumor at the base of the heart.

The dark red jelly-like material is
the tumor at the base of the heart.


The radiograph shows what appears to be very large heart.

The radiograph shows what appears to be very large heart. In fact, the sac surrounding the heart is full of fluid.  The heart is centered inside the fluid where it is being compressed by the pressure of the fluid. Because soft tissue and fluid looks the same on the radiograph, it is not possible to distinguish the heart from the fluid around it.



SURGERY ALONE: Unless the hemangiosarcoma is superficial in the skin and can be completely removed before it invades the deeper tissues under the skin, surgery alone is not going to be very satisfying. While removing the spleen, affected liver lobes, right auricle of the heart or other area where the main tumor is located will control the cycle of bleeding and clotting, it will not meaningfully alter the progression of the cancer. Survival times are typically 1-3 months for surgery alone.

FOLLOWING SURGERY WITH CHEMOTHERAPY: Survival times for surgery followed by chemotherapy typically range from 140-200 days. Combinations of doxorubicin, cyclophosphamide, and vincristine are typically used with no protocol distinguishing itself as superior to the others so far. A new medication called Toceranib phosphate (Palladia®) is being investigated for use against this tumor and results are promising. The field of veterinary oncology is fast moving so for the most up to date statistics and options, it is best to see a veterinary oncologist.

SKIPPING SURGERY AND JUST USING CHEMOTHERAPY: It seems intuitively bad to leave a large potentially bleeding cancer in place and attempt to attack it with medication only but in one study doxorubicin alone yielded a good response in approximately 40% of patients with inoperable hemangiosarcoma (range of survival was 13-190 days). Some of the dogs responded as well as those that had both surgery and chemotherapy.

RADIOTHERAPY AS AN ADJUNCT TO CHEMOTHERAPY: This is only an option for hemangiosarcomas in the muscle or under the skin as those in the abdomen or heart are too deep. In a study of 20 dogs, 70% experienced shrinkage of the tumor, 20% experienced complete (though temporary) resolution of the tumor, and the median survival time was 95 days.

ON THE HORIZON: Immunotherapy is an active area of research with the idea being to find a vaccine that will induce the patient's own immune system to seek and attack the tumor. This area appears very promising but is still in an experimental stage. Antiangiogenic therapy involves reducing the tumor's ability to generate blood vessels to feed itself. This area is also investigational at this time. It may be possible for your pet to participate in a funded study. Your oncologist can direct you.



As cancers go in cats, hemangiosarcoma is not a common one as it is for dogs but cats still can get hemangiosarcomas. There appear to be four main types of hemangiosarcoma in cats:

  • Dermal (in the skin)
  • Subcutaneous (under the skin)
  • Visceral (involving internal organs)
  • Oral (usually growing from the gums)

orange cat


Recent studies indicate that the dermal and subcutaneous forms are the most common. These forms have a predisposition to developing on the head, which suggests that sun exposure is a risk factor. For the dermal and subcutaneous forms of feline hemangiosarcoma, surgical removal is the chief form of therapy and is the most likely to be curative for dermal forms. Subcutaneous hemangiosarcomas are more difficult to remove completely and have a 60% recurrence rate after surgery. The visceral form is the most aggressive form with approximately 30% of cats being far gone enough to warrant euthanasia at the time of initial diagnosis (or having already died with the diagnosis being made on a post-mortem exam).

In dogs, adding chemotherapy to surgery has been helpful in extending the disease-free interval. Certainly protocols are available for cats, but so few cats have been treated that statistics comparing protocols or even comparing surgery plus chemotherapy treatment vs. surgery alone are not available.

One useful finding that has emerged from retrospective studies is the significance of the mitotic figure count on the biopsy sample. A mitotic figure is a cell that is in the process of cell division when it is fixed in formaldehyde. Since rapid cell division is a feature of malignancy, the number of mitotic figures seen on a slice of tissue can indicate how aggressive a tumor is. Apparently more than 3 mitotic figures per high power microscope field indicates a much shorter survival time than would be achieved in a case with a smaller number of mitotic figures. The mitotic figure count is reported by the pathologist when the biopsy sample is read, although it may have to be specifically requested.




 Page last updated: 11/4/2014