Hemangiosarcoma (HSA) is a highly aggressive, malignant cancer originating from endothelial cells, which line the blood vessels. Because of its vascular nature, HSA can develop anywhere blood vessels are present, but it most often affects internal organs. It is one of the most serious and common cancers in dogs. HSA often progresses silently, showing few obvious symptoms until the disease is advanced or a life-threatening event occurs.
The Nature of Hemangiosarcoma
HSA tumors are derived from vascular endothelial cells, though some research suggests they may originate from a bone marrow progenitor cell. This cellular origin results in fragile, blood-filled masses prone to rupture and hemorrhage. The disease occurs most frequently in middle-aged to older dogs, typically those over six years old, with the median age of diagnosis around ten years.
The primary sites for visceral hemangiosarcoma are the spleen and the right atrium of the heart. The spleen is the most common location, and approximately 50% of splenic masses are malignant hemangiosarcomas. HSA also appears in the liver and, less commonly, as cutaneous or subcutaneous tumors on the skin.
Certain large breeds carry a significantly higher genetic risk. Golden Retrievers and German Shepherd Dogs are highly susceptible, along with Labrador Retrievers and Boxers. For Golden Retrievers, the estimated lifetime risk is as high as one in five, making it a leading cause of cancer-related death within the breed.
Recognizing the Warning Signs
The clinical signs of hemangiosarcoma are linked to the tumor’s tendency to bleed, ranging from subtle, intermittent leakage to catastrophic internal hemorrhage. Since the tumors are fragile, they frequently leak blood into the abdominal or chest cavity. This chronic blood loss causes vague, waxing and waning symptoms often mistaken for normal aging.
Subtle signs include increased lethargy, tiredness after light exercise, or a mild decrease in appetite over several weeks. Owners might notice their dog seems “off” for a day or two, only to appear normal once the body reabsorbs the leaked blood. These nonspecific symptoms can indicate chronic anemia and internal blood loss.
The most alarming signs occur when a tumor ruptures completely, causing acute, severe internal bleeding and a medical emergency. Acute events manifest as sudden weakness or collapse, difficulty breathing, and a visibly distended abdomen. The dog’s gums may appear very pale or white, signaling profound blood loss and shock.
Diagnostic Procedures and Treatment Pathways
Diagnosis often begins with imaging, using ultrasound and X-rays to visualize internal tumors. Abdominal ultrasound identifies masses on the spleen or liver, and chest X-rays check for metastasis, particularly to the lungs. If internal bleeding is suspected in an emergency, a veterinarian may perform an abdominocentesis (“belly tap”) to collect abdominal fluid; non-clotting blood strongly suggests a bleeding tumor.
A definitive diagnosis requires histopathology, the microscopic analysis of a tissue sample obtained via biopsy or surgical removal. Cytology (fine-needle aspiration) is often unreliable for HSA because the sample is frequently contaminated with blood, making it difficult to distinguish malignant cells. Once confirmed, treatment typically involves a multi-modal approach combining surgery and subsequent chemotherapy.
Surgical intervention is often the immediate, life-saving measure, especially if the tumor has ruptured. For splenic tumors, a splenectomy (removal of the entire spleen) is performed to stop the hemorrhage and remove the primary tumor. Surgery for cardiac tumors, such as a mass on the right atrium, is more complex and may involve relieving pressure around the heart caused by accumulated blood.
Following surgery, adjuvant chemotherapy is the standard of care to target microscopic disease that has spread. Doxorubicin-based protocols are the most common regimen used to delay metastasis. When aggressive surgery or chemotherapy is not feasible, palliative care options, such as metronomic chemotherapy (low-dose, frequent oral chemotherapy) or supportive supplements like Yunnan Baiyao, may be used to manage the disease and improve comfort.
Prognosis and Quality of Life Management
Hemangiosarcoma carries a guarded to poor prognosis due to its aggressive nature and high metastatic rate. For visceral forms, the outcome depends on the tumor location and the extent of treatment. Dogs treated with surgery alone for a splenic tumor typically have a median survival time (MST) of approximately one to three months.
Adding an appropriate chemotherapy protocol after surgery can significantly extend this period, with MSTs generally ranging from five to seven months. Dogs with cutaneous hemangiosarcoma, which has not spread beyond the skin, often have a much more favorable prognosis. For these patients, MST can be significantly longer, sometimes exceeding 200 days, especially if the tumor is completely removed.
Managing quality of life is paramount after diagnosis, focusing on comfort and maximizing remaining time. Supportive care includes closely monitoring for signs of re-bleeding, such as sudden weakness or lethargy, and administering medications to manage pain or anemia. Maintaining hydration and providing nutritional support are essential components of ongoing care.