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Encyclopedia of Canine Veterinary Medical Information 
Hemangiosarcoma
Hemangiosarcomas are a form of cancer which originates in the endothelium, which is the lining of blood vessels and spleen. As might be expected of a tumor arising in the blood system they are highly malignant and can be found almost anywhere in the body since blood vessels are necessary in almost all body tissues. There is a strong predilection for the spleen, pericardium and heart. These tumors are most common in middle aged or older dogs which are medium sized or larger but can occur in any breed. German shepherds are reported to be more susceptible to this tumor than most dog breeds. In our practice golden retrievers also seem to have a higher than normal incidence.
Because these tumors arise in internal organs there is often little warning that they are present prior to time they cause severe clinical signs of disease. A common estimate of the average time from discovery of the tumor until death occurs in affected dogs is six to eight weeks but death occurs more rapidly than this in a number of cases.
Visible bleeding, usually in the form of nosebleeds, and signs associated with blood loss, such as tiring easily, episodes of unexplained weakness, pale color to the mucous membranes of the mouth and eyes, increased respiratory rates, abdominal swelling and depression are the most common presenting signs for patients with hemangiosarcoma. A few dogs just suddenly die with no clinical signs having been noted by their families prior to death. Bleeding disorders associated with hemangiosarcoma are sometimes confused with immune mediated hemolytic anemia (IMHA) because the type of anemia caused by the two conditions is very similar and early clinical signs are often very similar, as well. Hemangiosarcomas can cause very large tumors, sometimes as large as ten or more pounds, when they affect the spleen.
In most instances tumors of this size in this location are found on physical exam. In other cases the tumor affects the heart and is hard to find on a physical exam and even easy to miss or X-rays. Sometimes there are hundreds of small tumors spread throughout the body and surgical exploration or an autopsy are the only ways to identify the problem.
The blood disorder that most commonly accompanies the presence of hemangiosarcoma tumors is disseminated intravascular coagulation (DIC). This is blood clotting that is occurring inappropriately inside the blood vessels. It uses up all of the blood clotting elements rapidly and dogs with this condition usually have platelet deficiencies, increased blood clotting times, decrease in fibrin content in the blood and an increase in fibrin degradation products (FDPs). This is probably the cause of death in most dogs affected with hemangiosarcoma.
Diagnosis of hemangiosarcoma can be accomplished in a number of ways.Identification of a tumor in the spleen or heart raises a high degree of suspicion for this tumor. Abdominal swelling is also highly suggestive in an older large breed dog. If fluid is aspirated from the abdomen and it looks like blood it is even more suggestive of hemangiosarcoma. If blood is drawn and will not clot when left in the syringe it is another sign that a dog may have this tumor. In some cases careful evaluation of the type of bleeding disorder present is necessary to raise the suspicion of
hemangiosarcoma.If a tumor is identified when it is small it may be possible to remove the spleen if the tumor is there or even to remove tumors found near the heart and prolong the pet's life. Most of the time this will not make much difference, though. These are highly malignant tumors and most have spread by the time they can be identified. To the best of my knowledge there is not a very successful hemotherapeutic or radiation protocol for this cancer at this time but dogs treated with chemotherapeutic agents do live a little longer than dogs that do not receive this treatment.
Treatment for the bleeding disorders and aggressive supportive care also prolong the life of patients with hemangiosarcoma. If treatment for IMHA or immune mediated thrombocytopenia (ITP) are instituted due to confusion over the underlying cause of clinical signs early in the diagnostic process there is not likely to be any harm to the dog.
Due to the tendency to look for an inciting agent in IMHA and ITP it is a good idea to consider an autopsy exam if a dog dies before a definite diagnosis of any of these conditions can be made. Finding hemangiosarcoma saves a lot of agonizing over possible causes of the death of a friend. There are no known predisposing factors other than size and breed that I am aware of for hemangiosarcoma.
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Last edited 01/13/08