Sarcomas are cancerous tumors that arise from the cells of blood vessels, nerves, muscles, connective tissues or fat. They are usually malignant, which means that they tend to worsen with time. Sarcomas can cause serous illness and, eventually, death. They typically grow slowly and spread (metastasize) only after they have been growing in one place for quite some time. Sarcomas can be well-defined and encapsulated, or they can have indistinct borders that infiltrate nearby areas, much like the tentacles of an octopus probing into surrounding tissues. Together, all the different types of sarcomas account for about 15% of recognized cancers in companion dogs.
Hemangiosarcoma is a particular type of sarcoma that arises from cells lining blood vessels – especially the smaller arteries and veins. The lining of blood vessels is called "vascular endothelium." Arteries are the vessels that carry oxygenated blood from the heart and lungs to the rest of the body. Veins are the vessels that carry unoxygenated blood and waste products from body tissues back to the heart and lungs. Since hemangiosarcomas involve abnormal overgrowth of blood vessel tissues, they tend to bleed profusely when they are cut or disturbed. They are particularly fragile tumors that are prone to rupturing and causing internal bleeding that can be extremely dangerous - and often fatal - to the affected animal.
Other names for hemangiosarcoma are HAS, angiosarcoma and hemangioendothelioma. Hemangiosarcomas are common in dogs and rare in cats. Unlike some of the other canine sarcomas, hemangiosarcomas are very invasive, fast-growing tumors that often migrate to the spleen, heart, liver, lungs, kidneys, muscle, lymph nodes or skin. Usually, by the time hemangiosarcoma is diagnosed, it has already spread from its initial site to other places in the dog's body.
Causes of Hemangiosarcoma
The actual causes of hemangiosarcoma, like the causes of most other types of cancer, are not well understood. Hemangiosarcomas can develop anywhere on the surface of a dog's body, inside its internal organs or within body cavities. Primary hemangiosarcomas tend to occur most frequently in the skin, heart, spleen, liver and bone. Wherever they start, hemangiosarcomas initially are formed from cells lining small blood vessels. They are predisposed to spreading rapidly to remote areas of the dog's body. This is referred to as "metastasis," or "seeding of the cancer."
Hemangiosarcoma of the heart is one of the most common cardiac cancers in companion dogs. The causes of hemangiosarcoma that develops inside a dog's body, such as in or around the spleen, liver, heart and bones, remain a medical mystery. However, the fact that certain breeds and sizes of dogs are predisposed to developing hemangiosarcoma strongly suggests that there is a genetic component to its cause. Hairless areas of a dog's skin, like the belly and inner thighs, are prone to developing dermal, or cutaneous, hemangiosarcomas. The terms "dermal" and "cutaneous" refer to the skin. Dogs with this type of hemangiosarcoma often have a history of prolonged exposure to sunlight. Dermal hemangiosarcoma usually shows up as a solitary tumor and is not as likely to spread – or to metastasize – as other types of this cancer. Hemangiosarcoma can also occur in the subcutaneous areas just under the skin; this form of the disease is not thought to be associated with ultraviolet light exposure.
Prevention of Hemangiosarcoma
To reduce the risk of hemangiosarcoma of the skin, lightly colored dogs, short-haired dogs and dogs with especially thin haircoats should not be left out in the sun for long periods of time without being provided with some source of shelter. There is no known way to prevent internal hemangiosarcoma from forming and spreading. Certainly, feeding a high-quality diet and having fresh water freely available can help to promote a long, healthy, and hopefully disease-free life. It is also a good idea to have companion dogs seen by a veterinarian regularly for check-ups and vaccination boosters. Routine blood work, a urinalysis and a thorough physical examination, done annually, can identify diseases or disorders of the kidneys, liver, spleen, adrenal glands, heart, lungs, thyroid gland and other vital organs, even before the dog's owner sees any symptoms of illness.
Early identification of medical problems is one of the best ways to prevent or delay progression of the condition and improve the dog's chances of partial or complete recovery. However, until the actual causes of hemangiosarcoma are better understood, this invasive and often deadly type of cancer will to continue to haunt owners of companion dogs.
How Hemangiosarcoma Affects Dogs
While it is difficult to say with certainty how a dog with hemangiosarcoma is affected by its condition, reports from people with this disease, and observations of dogs, suggest that hemangiosarcoma usually causes a great deal of discomfort and pain, especially in the later stages. The exact symptoms will depend upon the site of the primary tumor (liver, spleen, heart, skin, bone, other), and where the cancer has spread.
Symptoms of Hemangiosarcoma
Owners of dogs with hemangiosarcoma may notice a number of different symptoms, depending upon where the cancer started and the extent to which it has metastasized. Often, the initial signs of hemangiosarcoma are chalked up to old age, changes in weather or alterations in the dog's living environment. However, once the disease advances, the obvious physical deterioration associated with hemangiosarcoma usually develops very rapidly. This may include:
Visible lumps on the legs, head, face, ears, prepuce, muzzle, back, ribs, abdomen, flank area, belly or elsewhere; hemangiosarcoma of the skin ("cutaneous" or dermal tumors) often develop on lightly-haired areas of the belly and inner thighs; they tend to be raised, smooth, firm, solitary and dark red in appearance, although this is not always the case
Weakness (progressive or intermittent, often with seemingly spontaneous recovery)
Exercise intolerance (usually mild)
Lack of appetite (inappetance; anorexia; usually starts mildly and progresses as the cancer spreads)
Collapse (usually acute; happens without warning)
Difficulty breathing (dyspnea; respiratory distress; caused by internal bleeding from rupture of tumors that have spread to the lungs or chest cavity)
Abnormal heart rhythms (arrhythmias)
Elevated heart rate (tachycardia)
Muffled heart sounds
Enlarged liver (hepatomegaly)
Enlarged spleen (splenomegaly)
Pale mucous membranes (pallor; especially of the gums)
Excessive formation and excretion of a large amount of urine (polyuria)
Excessive thirst and intake of water (polydipsia)
Blood clotting abnormalities
Sudden death; usually results from uncontrollable bleeding caused by rupture of a hemangiosarcoma tumor, which causes the dog to bleed to death from internal hemorrhage
Dogs at Increased Risk
German Shepherd Dogs, Golden Retrievers, Boxers, Great Danes, English Setters and some other large breed dogs are particularly predisposed to developing certain forms of hemangiosarcoma. Short-haired dogs, like the Whippet, Dalmatian, Pointer, Greyhound and Pit Bull, are also predisposed. The reasons for these breed associations are not well-understood, but they do suggest a genetic component to this type of cancer. Hemangiosarcoma affects middle-aged and older dogs more commonly than it affects younger dogs.
How Hemangiosarcoma is Diagnosed
Hemangiosarcoma is usually diagnosed using X-rays (radiographs), ultrasonography (ultrasound), computed tomography (CT scan) and tissue biopsies of suspicious masses. Chest X-rays are especially useful to determine whether the cancer has spread to the lungs. Abdominal X-rays and abdominal ultrasound can also reveal spread of the cancer, especially if they show an enlarged liver or spleen. Of course, a complete history and a thorough physical examination are critical parts of the diagnostic process. The abdomen will be palpated (felt) for internal masses. This will be done gently and extremely carefully, to avoid disrupting and potentially rupturing any fragile hemangiosarcoma tumors.
Routine blood work, including a complete blood count and a serum biochemistry profile, may reveal abnormally low levels of circulating red blood cells; this condition is called "anemia." This can happen if a hemangiosarcoma tumor ruptures, which will cause blood to leak from the organ or tissue affected by the mass and reduce the amount of healthy red blood cells circulating throughout the dog's body. Blood clotting times are prolonged when internal bleeding occurs. These abnormalities can be assessed by performing blood coagulation profiles.
If hemangiosarcoma is suspected, the attending veterinarian may recommend taking samples of fluid from the dog's abdomen and/or chest. This can be done fairly easily by inserting a sterile needle into the body cavity and aspirating a sample by pulling back on the plunger of the attached syringe. Free blood in the belly or chest is not normal. However, when a hemangiosarcoma tumor ruptures, blood will flow from the burst blood vessels into body cavities, where it is not supposed to be present. Echocardiography can be used to evaluate the heart, although very small masses may not be able to be seen using this procedure.
The gold standard for diagnosing hemangiosarcoma is surgical biopsy of suspicious tissue masses. If the spleen is enlarged and appears to be involved, it probably should be removed in its entirety and submitted to a laboratory for diagnostic evaluation.
Most hemangiosarcoma tumors are quite large by the time they are discovered. They also usually have already spread to other parts of the dog's body by the time that they are diagnosed.
The main goals of treating hemangiosarcoma are to remove the tumors surgically if possible, minimize the chances of bleeding from tumor rupture and prolong the dog's survival time and quality of life. If the cancer has spread to the spleen, that organ can be removed by a splenectomy. Unfortunately, depending upon the extent of local invasion of the cancer into surrounding areas, it is not always possible to remove all of the cancerous tissue. Radiation, chemotherapy and medically-induced elevation of body temperature ("managed hyperthermia") are other available techniques that can be used to treat – or at least to manage - hemangiosarcoma. While these techniques may help to prolong a dog's life, they almost never accomplish a complete cure. This is true even if the tumors are removed before there is any detectable evidence that the cancer has spread.
Chemotherapy involves administering highly toxic drugs directly into a dog's bloodstream through a vein (intravenously). These drugs target and kill rapidly-dividing cells, such as cancer cells. Unfortunately, current chemotherapeutic drugs cannot distinguish between cancer cells and other cells that normally reproduce rapidly, like cells that line the inside of the stomach, intestines and hair follicles. As a result, chemotherapy carries the risk of severe side effects, including nausea, weakness, hair loss, and perhaps even death.
A dog diagnosed with hemangiosarcoma deserves nurturing and kind supportive care, whether or not surgery, chemotherapy or other treatments are attempted. This might include administration of intravenous fluids to keep the dog well-hydrated. Blood transfusions, corticosteroid medications and/or antibiotics may be appropriate, depending upon the particular dog's condition. Of course, a clean, warm, safe living environment, a high-quality diet and free access to fresh water are always important to a dog's comfort and overall well-being.
The prognosis for dogs with hemangiosarcoma is highly variable. It depends upon how advanced the cancer is, and when treatment begins. In most cases, the ultimate outcome is guarded to grave, especially when the tumors are internal (noncutaneous hemangiosarcoma). Dogs with internal hemangiosarcoma usually die within a few months after their disease is diagnosed. Survival longer than one year is extremely rare. Dogs with hemangiosarcoma of the skin (cutaneous), or layers just below the skin (subcutaneous), are less likely to have the cancer metastasize to other areas. Therefore, they have a much better chance of going into remission following surgical removal of their tumors.