Nancy McDonald, RN, BSN

Hemangiosarcoma, also known as malignant hemangiothelioma or angiosarcoma, is a very aggressive, high-grade soft tissue cancer of vascular tissue with the skin, heart and spleen the most common areas affected.  Dermal (skin) hemangiosarcomas are less aggressive than visceral tumors with lower metastatic potential and longer survival times.  Visceral (internal) tumors are highly malignant tumors with a poor prognosis. This highly malignant cancer originates in the lining of the blood vessels, spreads rapidly, causing tumors almost anywhere in the body.  Insidiously, it attempts to build its own blood vessel network, making blood-blister-like formations which disrupt normal organ function.  A common form of cancer in dogs, hemangiosarcoma affects mostly older, large breed dogs although all dogs, including young, can be affected.  Males tend to have a higher rate of diagnosis than females, with German Shepherds, Portuguese Water Dogs and Golden Retrievers more affected than other breeds.  Because hemangiosarcoma occurs more commonly in dogs than other animals and is more frequent in some breeds, inheritable-risk-factors with environmental factors probably lead to the range of possible mutations at the genetic level that gives rise to the tumor.  This cancer has not been reported in large numbers in Bichons, although it has occurred.

Dermal (skin) hemangiosarcoma often appears as a rosy red or purple to black growth on the skin, which may be raised.  Associated with sun exposure, this form of tumor tends to appear on non-haired or sparsely haired areas like the abdomen.  Dogs with short white-haired fur (such as Dalmatians, Whippets, Italian Greyhounds, Bull terriers) are prone to this tumor development. Although solar-induced canine dermal hemangiosarcomas generally do not have as aggressive biologic behavior as visceral tumors and can be controlled with topical chemotherapy as needed, numerous lesions may continue to appear over a period of several years.   Because 30% of all dogs with dermal hemangiosarcoma develop metastatic disease, it is important to remove the growths promptly.

The overlying skin on top of a hypodermal (under the skin) hemangiosarcoma is often totally normal.  When the tumor is removed, a dark red blood growth is found.  Because 60% of hypodermal hemangiosarcomas spread internally, it is important to run further tests, chest x-rays, ultrasound of the abdomen, and ultrasound of the heart to determine if the cancer has spread.

Visceral (internal) hemangiosarcoma accounts for 2% of all reported malignancies and up to 5% of all noncutaneous tumors in dogs.  Although these numbers seem small, the impact is significant since this form of cancer kills.  The spleen and right atrium of the heart are the most common sites of occurrence of visceral hemangiosarcoma.  The spleen is seated deeply within the abdomen and tends to go unnoticed unless it develops a growth of unusual size.  Because the spleen is especially vascular, any growth, regardless of whether it is benign or malignant, has a tendency to break open and bleed profusely.  If the splenic tumor is found early and is not too large, a splenectomy (removal of the spleen) may be preformed.  Although a splenectomy certainly protects from this life-threatening sudden bleed, splenic hemangiosarcoma is still a rapidly spreading malignancy. 25% of dogs with splenic hemangiosarcoma also have a heart-based hemangiosarcoma.

Like the splenic hemangiosarcoma, the heart-based hemangiosarcoma tends to exert its life-threatening effects by bleeding.  The heart is enclosed in a sac called the “pericardium.”  When the hemangiosarcoma bleeds, the blood fills up the pericardium creating so much pressure that the heart can no longer function.  If allowed to progress, results are a circulatory collapse called a “pericardial tamponade” and can only be relieved by withdrawing the excess fluid from within the pericardium.  At the time the heart-based hemangiosarcoma is discovered, 63% have evidence of metastatic tumor.

The most common blood disorder associated with hemangiosarcoma tumor is disseminated intravascular coagulation (DIC), blood clotting that occurs inappropriately inside the blood vessels.  This process uses up all the blood clotting elements rapidly.  Dogs with this condition usually have platelet deficiencies, increased blood clotting times, decreased fibrin content in the blood and an increase in fibrin degradation products.  This is the cause of death in most dogs affected with hemangiosarcoma.  Bleeding disorders associated with hemangiosarcoma are sometimes confused with immune-mediated hemolytic anemia because the type of anemia caused by the two conditions is very similar and early clinical signs are often very similar.  Also, due to the thrombocytopenia (platelet deficiency), immune-mediated thrombocytopenia may be suspected.

Visceral hemangiosarcomas leave little warning they are present prior to causing severe clinical signs of disease.  A common estimate of the average time from discovery of the tumor until death occurs is six to eight weeks, but death occurs more rapidly than this in some cases.  Visible bleeding, usually in the form of nosebleeds, and signs associated with blood loss, such as tiring easily, episodes of unexplained weakness, pallor to the mucus membranes of the mouth and eyes, increased respiratory rates, abdominal swelling and depression are the most common presenting signs for hemangiosarcoma.  A few dogs just suddenly die with no clinical signs having been noted.  A large splenic hemangiosarcoma can be found on physical exam.  Heart-based hemangiosarcoma is hard to find on physical exam and can be missed on x-rays.  If bloody fluid is aspirated from the abdomen, hemangiosarcoma is suspected. Sometimes hundreds of small tumors are spread throughout the body, and surgical exploration or an autopsy are the only ways to identify the problem.

Hemangiosarcoma is primarily treated with a combination of surgery and chemotherapy and some radiation.  The drug of choice is Doxorubicin and Cyclophosphamide.  Surgical removal alone is often not very rewarding.  Because of the high risk of metastasis, the average survival time without chemotherapy is one to two months, with less than 10% of these dogs living a year.  With surgical removal and accompanying chemotherapy, the average survival time increases to five to seven months.  However, 90% of theses dogs still do not survive more than a year after initial treatment.  Skin-based hemangiosarcoma appears less likely to be metastatic when initially diagnosed, and surgical removal of the skin-based tumors can be curative.  However, chemotherapy is often recommended in addition to surgery.

In summary, hemangiosarcoma tumors cause significant bleeding extra-vascular (outside the blood vessels) and clotting intra-vascular (within the blood vessels) and spread early; survival times are usually short.  Surgery is helpful to prevent massive blood loss, but rarely affords a cure.  Chemotherapy can be helpful, but even with aggressive treatment survival beyond one year is extremely rare.  Only superficial skin tumors allow long-term survival with surgery alone, although recurrence is likely.  Recently, some fundamental properties of canine hemangiosarcoma, unique patterns of protein expression, have been identified that may lead to the development of new chemotherapy drugs in association with early detection to increase survival time.  In addition, recent data from the Modiano Lab supports the idea that the disease is of stem cells, the first such evidence for a canine tumor.  Work there is focusing on characterizing these stem cells, as their unique properties may lead to highly targeted, non-toxic therapies to effectively treat this disease.  Because hemangiosarcoma is rare in humans little research funds have been allocated toward this disease thus improvements in early detection and treatment is slow.

Heritability contributes to the risk of developing hemangiosarcoma so it may be possible to reduce the incidence by removing the highest risk alleles from the population.  Research by Dr. Elaine Ostrander and Dr. Kerstin Lindblad-toh seek to map risk alleles in Portuguese Water Dogs, Golden Retrievers, and German Shepherds using resources made available by the recent completion of the Canine Genome Project.

Dr. Matthew Breen seeks to determine breed specific abnormalities that are detectable in tumors obtained from dogs of different breeds.  Data from this project shows that tumors from dogs of one specific breed are functionally and genetically more similar to each other than they are to tumors from dogs of other breeds.  This will provide tangible evidence that heritable risk factors are a contributor to the development of canine cancer.

American Kennel Club/Canine Health Foundation has fifteen grants dedicated to work on finding cause and treatment for canine hemangiosarcoma.

Jaime F. Modiano, VMD, PhD, Michelle G. Ritt, DVM, DACVIM, Matthew Breen, PhD, Cbiol, MIBiol, and Tessa Breen, BSc (Hons), Dip GD, CMM, University of Minnesota, St. Paul, MN (JFM & MGR), and North Carolina State University (MB TB), “Canine Hemangiosarcoma – The Road From Despair to Hope”, Discoveries American Kennel Club Canine Health Foundation, Issue 24, Winter 2007, pp 3, 5, 8, 9

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Reviewed: 2016