Hemangiosarcoma is a cancer that, in the most serious variety, is almost always fatal in dogs because it is so difficult to detect before it has reached the life-threatening stage. Historically the prognosis for the disease is not good because by the time it is diagnosed there were no treatment options and the dog typically died within six to eight weeks after the diagnosis. With new methods for testing for the cancer as well as drug therapies and chemotherapy the disease, while still very serious, is often not fatal if detected early.

There are three different types of hemangiosarcoma found in dogs. The two easiest to detect type occur in and on the skin. Dermal hemangiosarcoma is a typically purplish discoloration of the skin usually seen on the belly area of the dog where the hair is the lightest. The tumor may be slightly raised or may seem to be relatively flat to the skin. This type of cancer is highly malignant and will travel throughout the body so early surgical removal is essential to controlling the spread of the cancer. Usually surgical removal of dermal hemangiosarcoma is effective and the dog will recover fully if the cancer has not spread. About a third of all dogs diagnosed with dermal hemangiosarcoma will develop another form of cancer in their life.

The second type of hemangiosarcoma is the hypodermal or under the skin tumor. This can be a soft to hard mass or cyst-like growth that is under the skin but may become an open ulcer or lesion as it develops. The mass may be located anywhere on the dog but is most commonly found on the neck, chest and trunk of the dog. Almost two thirds of all dogs with hypodermal hemangiosarcoma will develop another form of cancer or the hemangiosarcoma will spread to the internal organs. Surgical removal of the tumor along with chemotherapy is often successful with these dogs provided it is detected and treated early.

The most serious and rare form of hemangiosarcoma is the visceral type. While only accounting for about 5% of the total tumors removed from dogs, it is the most fatal. The cancerous tumors are found on the heart and spleen and in many cases will metastasize or spread to the brain and lungs, resulting in death. Often the tumors can be several pounds in weight and produce a huge strain on the heart and circulatory system, further complicated if the dog is obese, old, or has other health conditions. Tumors that cause ruptures to the spleen or impair the heart function can result in undiagnosed death of the dog and would only be discovered if an autopsy were completed.

The early signs of the visceral type of hemangiosarcoma include weight loss, bleeding from the nose or mouth, lack of energy, lack of appetite, pale gums, despondency and swelling of the abdominal area. Since these conditions are often mistaken for other blood conditions such as hemolytic anemia they can easily be misdiagnosed and only discovered if specific x-rays of the spleen and heart are completed.