Overview

Hemangiosarcoma (HSA) is a highly malignant cancer of blood vessels, most commonly affecting the spleen or heart of older, large breed dogs. HSA may have little to no signs early on or can present as an emergency after a sudden episode of collapse. HSA tends to rapidly spread (metastasize) to other parts of the body, most commonly the lungs and other abdominal organs like the liver. Unfortunately, the prognosis for HSA is often poor due to its aggressive nature. While there is no cure for HSA, surgery and chemotherapy may help delay cancer progression.

Cause

HSA originates from cells that normally create blood vessels (vascular endothelium). The spleen is the most common site for HSA, but since this cancer arises from blood vessels, it can occur anywhere in the body. Other common locations include the heart, the liver, or the skin and muscle. Like many forms of cancer, the exact cause of HSA is unknown. Genetics likely contribute since HSA is more common in certain breeds, such as German Shepherds, Golden Retrievers and Labrador Retrievers. UV sunlight is thought to play a role in the development of the skin form of HSA, but not the visceral (internal organ) form. While more commonly found in older animals, HSA can rarely occur in young dogs as well.

Clinical signs

Depending on the tumor location, dogs with HSA may show no clinical signs or mild, non-specific signs of illness, such as:

• Lethargy or weakness
• Exercise intolerance
• Decreased appetite

However, dogs with HSA of the spleen or heart are at risk of the tumor rupturing and bleeding, which often causes severe and often life-threatening emergent clinical signs such as:

• Collapse or severe weakness
• Rapid or difficulty breathing
• Pale gums
• Sudden death

HSA of the skin may appear as a bruising, “blood blisters,” or a more well-defined raised mass on the skin that can rupture and bleed outside of the body. If the mass is under the skin and in the muscle, external bleeding may not be apparent, but the area may appear more swollen or bruised. 

Diagnosis

Your veterinarian may suspect HSA if your dog presents after an episode of collapse with bleeding in their abdomen (hemoabdomen) or around their heart (pericardial effusion), or if a mass on the spleen or heart is incidentally discovered during a routine exam or ultrasound.

Initial testing may include imaging with abdominal ultrasound and x-rays (radiographs) of the chest and lungs or CT scan, and blood work to aid in diagnosing HSA and evaluating the extent or spread of the cancer and your dog’s overall health. An ultrasound of the heart (echocardiogram) may be performed to evaluate for the presence of a tumor in the heart’s right atrium that can be challenging to see on radiographs.

HSA is diagnosed definitively with a biopsy of the tumor if it is in a location that can be removed by surgery. Without a biopsy, a definitive diagnosis cannot be made, but hemangiosarcoma may be strongly suspected and considered the most likely cause.

Treatment

• Surgery and Chemotherapy: The ideal treatment of HSA involves surgery to remove the tumor before metastasis occurs, followed by chemotherapy to delay the progression of metastatic disease. If the tumor is on the spleen, a splenectomy (surgery to remove the spleen) is performed, which helps reduce the risk of potentially life-threatening internal bleeding from a ruptured tumor and can treat this bleeding if it occurs. Surgery is rarely possible for tumors on the heart.

  Chemotherapy often includes IV (intravenous) medications such as doxorubicin every three weeks for five treatments and frequent monitoring with blood work and imaging. Additional intravenous or oral chemotherapy options may also be available or recommended. 

  If metastasis is detected or surgery is not an option, chemotherapy may still be used to delay cancer progression but is often less effective in these circumstances.

• Radiation therapy may be considered instead of surgery when surgical removal is not an option or for a skin tumor that was incompletely excised to delay its recurrence, but systemic treatment with chemotherapy is often still recommended to delay metastasis.

• Supportive treatments: Some patients may require blood or plasma transfusions or IV fluids if significant blood loss occurs from tumor rupture. Other supplemental medications that may be suggested in addition to other treatments include: Yunnan Baiyao, which is a Chinese herb used in patients with bleeding conditions and I’m-Yunity, which is a turkey tail mushroom supplement.

Outcome

Unfortunately, there is no cure for splenic HSA and less than 10 percent of dogs will be alive one year after diagnosis. Microscopic metastatic disease is often unable to be seen on chest radiographs or abdominal ultrasound at the time of diagnosis. Surgery alone without chemotherapy is considered palliative, with an average survival time of two months, as the cancer aggressively comes back and causes bleeding in other organs in the abdomen and/or spreads to the lungs. If treated with chemotherapy after surgery, the median survival time can be increased to four to six months and treatment can help dogs maintain a good quality of life during that time. 

The prognosis for dogs with HSA of the heart is similar to that of splenic HSA. However, treatment may involve a combination of radiation therapy and chemotherapy since surgery is rarely possible in that location. 

The skin form of HSA has a variable prognosis depending on how deeply the cancer has spread. If HSA is confined to the skin, it may have a better prognosis and be treated with surgery alone. However, if the skin form of HSA extends more deeply into the muscle, it can behave as aggressively as the splenic and cardiac forms, in which case the treatment may involve a combination of surgery, radiation and chemotherapy.

Updated Oct. 2024