Hemangiosarcoma is a malignant, very aggressive form of cancer that forms anywhere in the body where there is blood supply, but it most usually forms on the skin, in soft tissues, or on the spleen or heart. It develops in the lining of a dog’s blood vessels, and can cause a fatal blood loss if the blood vessel ruptures. They spread very quickly, and can invade the skeletal muscles, kidneys, and brain. The three types are called visceral, hypodermal, and dermal.

Visceral hemangiosarcoma usually develops on the spleen, liver, or heart. Tumours of this sort that develop on the heart quite frequently  end with the dog collapsing and dying, without the owners even being aware there was a problem. A quarter of dogs with a tumour on the spleen also have a tumour on the heart.

Hypodermal hemangiosarcoma, also called subcutaneous hemangiosarcoma, occurs when the cancer develops just below the skin. Approximately 60 percent of this type of cancer spreads to internal organs.

Cutaneous hemangiosarcoma is easiest of the three to diagnose and treat, because it is visible on the surface of the dog’s skin. The tumour appears to be black or rosy growth, and will typically develop in response to excessive sun exposure, particularly on dogs with short, sparse, or white fur. About one-third of these cases is malignant and will spread to internal organs, so prompt removal and testing is necessary.

As mentioned, excessive sun exposure can cause the dermal form of this cancer, but it is unknown what causes the other two forms. Exposure to certain chemicals – like vinyl chloride, arsenic, and thorium dioxide – may be a factor, as it is in humans. These types of cancers may also be passed genetically, since there are several breeds that are at higher risk of developing hemangiosarcoma.

Dogs with little to no hair, or those with short white hair should be prevented from getting too much sun. This will help reduce the incidence of dermal growths. Dogs that develop any type of this cancer should not be bred in case of a genetic connection. Reduce the incidence of chemical exposures if possible. Immediate and aggressive treatment of dermal growths can help reduce the likelihood of the cancer metastasizing to other areas of the body.

When the tumour is internal, there are generally no outward signs until it ruptures and causes internal bleeding. Signs of internal bleeding include nosebleeds, lumps under the dog’s skin, unexplained depression, lethargy, pale mucous membranes, weakness, visible bleeding, difficulty breathing, seizures, abdominal swelling, abnormal heart rate, and collapse. Signs are very similar to those of anemia.

When the tumour is on the heart, the dog may show signs of exercise intolerance, weakness, difficulty breathing, build-up of fluid in the abdomen, and sudden collapse. Dermal tumours are usually visible and with subdural growths, you may feel a lump or mass under the surface, or see an ulcer above where the tumour is located.

Dogs at Risk
Dogs are at more risk to develop this cancer than any other species. It is more common in those between six and 13 years of age, although younger dogs can develop it. Mid- to large size dogs are at higher risk, particularly Golden Retrievers, Labrador Retrievers, German Shepherds, Dobermans, English Setters, Pointers, Dalmations, Great Danes, Poodles, Siberian Huskies, and Boxers. Breeds more prone to cutaneous hemangiosarcomas are white English Bulldogs, Salukis, Whippets, Beagles, English Pointers, Dalmations, and Bloodhounds. Gender does not impact the incidence of this type of disease; however, spayed and neutered dogs are at higher risk than unaltered dogs.

Testing and Diagnosis
The vet will take a thorough history of the dog’s health, perform a physical exam, and check for signs of anemia or internal bleeding. He or she will feel for abdominal swelling and may aspirate fluid from the abdomen. Further testing will include a complete blood count and chemistry panel, x-rays and/or ultrasounds of the chest and abdomen, ande urinalysis. Visible growths should be removed as soon as possible and analysed to determine if they are benign or malignant.

Treatment and Prognosis
Treatment and prognosis depends upon the location of the tumours. It is very likely that a dog will have multiple tumours and each one needs to be treated appropriately. Most dermal cancers, if caught soon enough, can be treated successfully by removal and radiation therapy. When the entire tumour is not removable due to location or involvement with internal organs, chemotherapy is often used.

Cases of cutaneous hemangiosarcoma where the cancer has not spread have a good prognosis. Dogs with tumours on the spleen, liver, or heart often show no symptoms and the cancer is not detected until the dog collapses, becomes gravely ill, or is tested for another problem that reveals the internal growths. Splenectomy – surgical removal of the spleen – will often give the dog another few months of life, but the prognosis remains grave, as it does when the tumour is located on the heart or other organs. Dogs with tumours on the heart may gain relief through aspiration of the pericardium.  Cases of visceral hemangiosarcoma are usually fatal.