A Vet’s Guide to Hemangiosarcoma: Understanding a Silent Cancer

Few cancer diagnoses are as sudden and shocking as hemangiosarcoma. Often, a pet seems perfectly healthy one moment and is in a state of critical collapse the next. It’s a heartbreaking and confusing experience for any pet owner. At Harmony Pet Clinic, we want to provide clear, compassionate information about this aggressive cancer to help you understand what is happening to your beloved companion.

What is Hemangiosarcoma?

Hemangiosarcoma (HSA) is a highly malignant cancer that arises from the cells lining the blood vessels. Because blood vessels are everywhere in the body, this tumor can technically form anywhere, but it has a strong preference for certain organs. These tumors are essentially fragile, blood-filled sacs that grow silently until they rupture, causing life-threatening internal bleeding.

Hemangiosarcoma in Dogs

This cancer is far more common in dogs than in cats, and certain breeds like Golden Retrievers, German Shepherds, and Labrador Retrievers are unfortunately predisposed. There are three main forms:

• Splenic Form: This is the most common form, where the tumor grows on the spleen.
• Cardiac Form: The tumor grows on the right atrium of the heart, which can interfere with heart function.
• Dermal/Cutaneous Form: This tumor forms on or under the skin. While still serious, the skin form often carries a better prognosis if it hasn’t spread internally.

Signs of Hemangiosarcoma in Dogs

The signs are almost always related to a tumor rupture and internal bleeding. This is a true medical emergency.

• Sudden, profound weakness or collapse.
• Very pale (white or gray) gums.
• A swollen, fluid-filled abdomen.
• Rapid breathing or panting.
• Unwillingness to get up.

Hemangiosarcoma in Cats

While much less common in cats, hemangiosarcoma does occur. Similar to dogs, it can be found in a cutaneous (skin) form or a visceral (internal) form, affecting organs like the spleen, liver, or intestines. The skin form in cats, especially if related to sun exposure on light-furred areas, may be less aggressive. However, the internal form is just as serious as it is in dogs and is treated with a similar emergency approach.

Diagnosis and Treatment

While many cases are diagnosed in a crisis, there is value in proactive screening, especially for at-risk breeds. Regular wellness exams that include senior blood work and imaging, such as abdominal x-rays or an ultrasound, are key to early detection. This can sometimes help us find a splenic mass before it has a chance to rupture, providing the best chance for a planned surgery and a better outcome.

Diagnosis in a crisis involves an ultrasound to find the source of bleeding and bloodwork to assess the level of blood loss. The immediate goal is to stabilize the patient with IV fluids and, if necessary, a blood transfusion.

The primary treatment is emergency surgery to remove the bleeding tumor, which most often means removing the entire spleen (a splenectomy). While this surgery can be life-saving in the short term, hemangiosarcoma has a very high rate of microscopic spread (metastasis). For this reason, chemotherapy is almost always recommended after recovery from surgery to help slow the spread of the disease and extend a good quality of life. The prognosis, even with aggressive treatment, is often guarded, making every moment of quality time precious.