Hemangiosarcoma in dogs is an aggressive, malignant tumor of blood vessel cells. With the exception of the skin form of hemangiosarcoma, a diagnosis of hemangiosarcoma is serious. Because these tumors start in blood vessels, they are frequently filled with blood and when a blood-filled tumor ruptures, it can cause problems with internal or external bleeding.
Hemangiosarcoma can theoretically arise from any tissue where there are blood vessels, which is essentially anywhere in the body, but usually appear in the skin, soft tissue, spleen or liver with the most common site being the spleen. They are highly metastatic and will frequently spread to the brain, but also to the lungs, spleen, heart, kidneys, skeletal muscle and bone. This type of cancer in dogs is typically classified as dermal, subcutaneous or hypodermal, and visceral.
The skin form of hemangiosarcoma are the most easily removed surgically and have the greatest potential for complete cure. The skin form looks like a rosy red or even black growth on the skin. This form is associated with sun exposure and thus tends to form on non-haired or sparsely haired skin (such as on the abdomen) or on areas with white fur. Dogs with short white haired fur (such as Dalmatians and pit bull terriers) are predisposed to the development of this tumor. Approximately 1/3 of cases will spread internally in the malignant way usually associate with cancer so it is important to remove such growths promptly. This form of menagiosarcoma is covered more broadly in the Skin Cancer section of this website.
Subcutaneous (hypedermal) Hemangiosarcoma
The overlying skin of a subcutaneous hemangiosarcoma is often completely normal. However below the skin is a dark red blood growth. Up to 60% of hypodermal hemangiosarcomas spread internally
Visceral Hemangiosarcoma – spleen
The spleen is a large abdominal organ which while not essential for life, serves an important role to the blood and lymph functions. Splenic growths have the unfortunate tendency to break open and bleed profusely regardless of whether they are benign or malignant. While a splenectomy (removal of the spleen) ends the prospect of this type of life-threatening sudden bleed, splenic hemangiosarcoma is still a rapidly spreading malignancy.
When a splenic mass is detected, it may not be possible to tell prior to splenectomy whether or not the mass is malignant or not although testing will most likely be performed to attempt to determine this. It has been estimated that 25% of dogs with splenic Hemangiosarcoma also have a heart-based Hemangiosarcoma.
Visceral Hemangiosarcoma – heart
Similar to splenic hemangiosarcoma, heart-based hemangiosarcoma tends to be life-threatening from the effects of bleeding. The heart is enclosed in a sac called the “pericardium.” When the hemangiosarcoma bleeds, the blood fills up the pericardium until it is so full that the heart inside is under so much pressure that it has no room to fill with the blood it has to pump. This is called pericardial effusion and must be treated before an emergent situation occurs.