2011 Hemangiosarcoma an Overview

HEMANGIOSARCOMA
an
OVERVIEW

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A diagnosis of Hemangiosarcoma (HSA) is disheartening. One day you have a seemingly healthy dog and days to weeks later it is gone. Hemangiosarcomas are highly malignant tumors which may involve spleen, right atrium of the heart, liver and other sites, multiple sites are possible. This tumor can also occur in skin in a less aggressive form. This malignancy arises from vascular endothelium (cells lining blood vessels) it is this association with blood vessels, that allows the rapid and widespread metastasis which is common with this disease. Metastasis occurs through blood vessels or locally through tumor rupture. Common sites of metastasis are lung, spleen, kidney and liver. The median age of dogs with HSA is 9 to 10.5 years. Hemangiosarcoma, occurs in all breeds, but there is a known breed predilection in German Shepherd Dogs, Golden Retrievers, Labrador Retrievers and Portuguese Water Dogs. Although it is not recorded in the literature, we know that it is not uncommon in the English Setter.

Clinical signs in dogs range from lethargy, lack of appetite, weight loss, abdominal swelling, difficulty breathing, acute weakness and collapse, depending on the organs involved. With splenic forms a dog may have a history of weakness or collapse followed by recovery in a few days. This is caused by rupture of the tumor and hemorrhage into the abdomen followed by resorbtion of these red blood cells. When there has been rupture of a tumor and hemorrhage tumor cells are spread throughout the abdomen. Twenty percent of dogs with splenic lesions will also have cardiac lesions. If a diagnosis is made prior to rupture of the tumor the potential for treatment and prognosis are somewhat improved.

Supportive care and diagnostic test performed may vary depending on the clinical signs in a given dog. Diagnostics will likely include blood test to determine the amount of hemorrhage, evaluate clotting factors and organ function, X-rays and abdominal ultrasound or echocardiography. Ultimately a tissue sample is needed to confirm the diagnosis. These tests will determine the spread of disease and the fitness of the patient for surgery and chemotherapy if warranted.

Unfortunately dogs with visible spread of disease will not benefit from treatment and sorrowfully euthanasia is usually recommended. Even dogs without visible signs of spread of disease at the time of diagnosis, most likely still have metastatic disease that will manifest in 1 to 3 months. The use of chemotherapy in these patients generally results in a modest improvement in survival times. In some cases the primary tumor can be removed surgically, this should be followed by chemotherapy. Presently chemotherapy can delay the manifestation of metastatic disease for 5 to 7 months with a survival rate of 10% at one year. The most commonly used drug is doxorubicin (Adriamycin). Five treatments are given at two week intervals. Several centers are using multi drug regimes with modest improvement in response. More information on hemangiosarcoma and other small animal cancers can be found on the CSU Animal Cancer Center website. www.CSUAnimalCancerCenter.org Another source of information on cancer in small animals is Withrow and MacEwen SMALL ANIMAL CLINICAL ONCOLOGY 4th Edition 2007 Saunders Elseviers

Although there are not any good treatment options for HSA at this time, laboratory studies are being conducted to elucidate novel approaches to HAS and other cancers. Among these novel approaches are inhalation chemotherapy for lung tumors and intracavitary chemotherapy for tumors of the abdomen Another novel approach is the isolation and characterization of antibodies that dogs produce against their tumors. These antibodies can then be used in targeted therapy. The goal of targeted therapy is the delivery of cytotoxic agents directly to tumor cells there by increasing the amount of drug received by the tumor while reducing systemic exposure and side effects from the cytotoxic agents. ESAA plans to sponsor one of these studies through the Canine Health Foundation.

The Canine Health Foundation currently sponsors studies in several laboratories which are ultimately directed at developing therapies or identifying genetic risk factors for hemangiosarcomas. Summaries of these studies can be seen at www.akcchf.org/research . Another approach being studied is agents to inhibit angiogenesis (new vessel formation). There are at least 15 known proteins which act on endothelial cells to promote new vessel growth and thereby promote tumor growth. There are also at least 20 known inhibitors of these promoters of angiogenesis. Other areas of study include immune system modulation and agents to inhibit metastatic disease. Further discussion of these studies is beyond the scope of this review. More information on these studies can be found in the following article CA Clifford et al. Treatment of Canine Hemangiosarcoma 2000 and Beyond, Jo Veterinary Internal Medicine 2000; 14:479-485. Most of these approaches are applicable to many tumor types in many species including man. Hopefully one of these approaches will lead to advancement in treatment of HSA and other cancers in man and dogs.

By Sharon Gillette PhD DVMu

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