Canine Hemangiosarcoma (Common in Spleen and Heart)

ImmunityDiseasesMeongsiljang Veterinary Advisory Board

Canine hemangiosarcoma is a malignant tumor that arises from the endothelial cells lining blood vessels, most commonly affecting the spleen and heart. Because early detection is difficult, it is often discovered only when sudden internal bleeding occurs in the abdominal cavity.

What is Canine Hemangiosarcoma?

A veterinarian performing an ultrasound examination on a senior Golden Retriever

Canine hemangiosarcoma is a malignant tumor arising from blood vessel endothelial cells (or their precursor cells), most commonly developing in organs with rich vascular networks such as the spleen, heart, liver, and skin. Its most frightening aspect is the difficulty of early detection. The tumor often grows silently without obvious symptoms, and many cases are only discovered when the tumor ruptures, causing sudden internal bleeding and collapse. Since hemangiosarcoma is more frequently reported in older dogs, it’s especially important to watch for signs of anemia or internal bleeding—such as pale gums—during the senior years, and to consult your veterinarian about whether regular check-ups are necessary.

Why Does It Commonly Occur in the Spleen and Heart?

Hemangiosarcoma arises from the abnormal proliferation of endothelial cells that line blood vessels. It most commonly occurs in organs with rich blood supply and complex vascular networks, such as the spleen, heart, and liver. Cardiac hemangiosarcoma, in particular, often presents as a single mass in the right atrium or right auricle, and may also occur simultaneously in the spleen. Although the exact cause remains unclear, breed-specific incidence patterns suggest a genetic predisposition, though this has not yet been definitively proven by specific studies. Indeed, German Shepherds, Golden Retrievers, and Labrador Retrievers have been reported to have a higher risk of developing visceral hemangiosarcoma.

Checklist of Main Symptoms

Hemangiosarcoma is characterized by a lack of symptoms until the tumor ruptures, at which point signs appear suddenly.

Sudden lethargy: A normally active pet may suddenly be unable to stand.

Pale gums: The normal pink color fades, leaving the gums pale or white.

Abdominal distension: The abdomen appears swollen and is painful to the touch.

Difficulty breathing: The pet may pant or breathe rapidly and with effort.

Petechiae on the gums: Small red spots appear on the gum tissue.

Fainting or collapse: The pet may lose consciousness for a few seconds.

A veterinarian’s hand checking a puppy’s gum color

Signs Requiring Immediate Emergency Care

If any of the following symptoms appear, seek immediate care at a 24-hour veterinary hospital. There is a high likelihood that a splenic tumor has ruptured, and shock can lead to death within hours. • Sudden pallor of the gums • Rapid abdominal distension • Collapse and inability to stand • Very rapid and shallow breathing • Body temperature lower than normal (feeling cold) During transport, keep your pet warm by wrapping them snugly, and handle them carefully to avoid putting pressure on the abdomen.

Diagnostic Methods

Hemangiosarcoma is diagnosed using a combination of tests. First, an abdominal ultrasound is used to identify masses in the spleen and liver, while an echocardiogram confirms the presence of cardiac tumors and pericardial effusion. A thoracic radiograph checks for pulmonary metastasis, and blood tests assess for anemia, thrombocytopenia, and coagulopathies. A definitive diagnosis can only be made through a biopsy, but due to the risk of hemorrhage, this is often performed during surgery. Veterinary internal medicine textbooks emphasize a comprehensive assessment integrating imaging findings and clinical signs.

Treatment Methods - Surgery and Chemotherapy

Treatment is generally divided into two main stages. Stage 1: Surgical Resection For splenic hemangiosarcoma, the standard procedure is a splenectomy, which involves removing the entire spleen. In cases involving the heart, surgery such as pericardiectomy or tumor resection is only performed if complete removal is feasible. Stage 2: Chemotherapy Even after surgery, microscopic metastases may remain, so a doxorubicin-based chemotherapy protocol is typically administered alongside surgical treatment. Studies report that combining splenectomy with adjuvant chemotherapy for splenic hemangiosarcoma results in a median survival time of approximately 141 to 179 days (about 5 to 6 months). However, because this is a highly malignant tumor with a strong tendency to metastasize, it is important to keep in mind that the overall prognosis remains poor despite treatment.

Veterinary medical team performing abdominal surgery on a puppy

Comparison of Survival Periods by Tumor Location

Item	Splenic hemangiosarcoma	Cardiac hemangiosarcoma	Cutaneous hemangiosarcoma
Incidence	Most common	Intermediate	Rare
Surgical resectability	Possible (splenectomy)	Limited (pericardiectomy, etc.)	Possible (excision)
Prognosis with surgery alone	Poor (adjuvant chemotherapy recommended)	Poor	Relatively good for solitary lesions
Median survival with surgery + chemotherapy	About 141–179 days (about 5–6 months)	Limited data · poor prognosis	Limited data
Early symptoms	Almost none	Exercise intolerance · fainting	Skin mass

The median survival time for splenic hemangiosarcoma with surgery plus adjuvant chemotherapy is reported to be about 141–179 days (per veterinary surgical oncology). Specific survival figures for cardiac and cutaneous forms are limited by available evidence.

Home Care Points

After diagnosis, daily care becomes the key factor in determining your pet’s quality of life.

Limit strenuous exercise: To prevent tumor rupture, allow only short walks.

Monitor appetite: Nausea and loss of appetite may occur during chemotherapy.

Ensure hydration: Adequate water intake is essential to reduce the burden on the kidneys.

Check body temperature: If your pet feels colder than usual, it may be a sign of internal bleeding.

Regular follow-ups: Schedule ultrasound and blood tests every 3 to 4 weeks after surgery.

An elderly dog resting comfortably at home with its owner

High-Risk Breeds and the Importance of Early Screening

The following breeds have been reported to have a higher risk of developing hemangiosarcoma, particularly the visceral form affecting organs such as the spleen and heart. Since hemangiosarcoma typically occurs in older dogs (with a reported average age of onset around 9–10 years), consider scheduling regular abdominal ultrasound screenings as your dog enters its senior years. • German Shepherd (high risk for visceral hemangiosarcoma) • Golden Retriever • Labrador Retriever Please note that brachycephalic breeds like Boxers are reported to have a predisposition to chemodectomas (tumors of the aortic body at the base of the heart) rather than hemangiosarcoma, so they require separate vigilance. For owners of senior medium-to-large breed dogs, making it a weekly habit to check your dog’s gum color can help you quickly detect signs of anemia or internal bleeding.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Is hemangiosarcoma curable?

In most cases, a complete cure is difficult. Because splenic hemangiosarcoma is highly malignant and often has already undergone microscopic metastasis by the time of diagnosis, the median survival time is reported to be approximately 141 to 179 days (about 5 to 6 months), even with splenectomy combined with adjunctive chemotherapy. However, the cutaneous (solitary) form has a relatively favorable prognosis if completely excised at an early stage.

Does a mass in the spleen always mean hemangiosarcoma?

Not necessarily. According to the "two-thirds rule," about two-thirds of splenic masses are malignant, and of those malignant tumors, roughly two-thirds are hemangiosarcomas. This means that hemangiosarcoma actually accounts for a smaller proportion of all splenic masses, and many cases turn out to be hematomas or benign nodules (such as nodular hyperplasia in senior dogs). Therefore, surgical removal followed by histopathological examination is necessary for an accurate diagnosis.

Are the side effects of cancer treatment severe?

During chemotherapy with drugs like doxorubicin, temporary side effects such as loss of appetite, vomiting, and diarrhea may occur. However, the type, severity, and recovery pattern of these side effects vary depending on the medication used and the patient’s condition, so it is safest to consult your veterinarian to adjust the chemotherapy schedule and manage side effects accordingly.

Are there any preventive vaccines or tests available?

There is currently no preventive vaccine available for hemangiosarcoma. However, for breeds prone to the disease, such as German Shepherds and Golden Retrievers, regular abdominal ultrasound screenings starting in their senior years can aid in early detection, considering the average age of onset is around 9 to 10 years.

How much does the treatment cost?

Treatment costs vary widely depending on the clinic, location, and tumor site, so it’s best to consult your veterinarian for an accurate estimate. Keep in mind that surgery, chemotherapy, and hospitalization fees are billed separately.

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References

[1] Withrow & MacEwen's Small Animal Clinical Oncology, 6th Ed - Chapter 34 Hemangiosarcoma

[2] Veterinary Surgical Oncology, 2nd Ed - Vascular Tumors

[3] Clinical Medicine of the Dog and Cat, 4th Ed - Vascular Tumors of Bone

[4] Notes on Canine Internal Medicine, 4th Ed - Hematologic Neoplasia