Haemangiosarcoma

Haemangiosarcoma (HSA) is one of the most insidious cancers in dogs. Insidious, because it arises from the cells of the blood vessel wall, grows unnoticed for a long time in internal organs and often only becomes apparent through a sudden emergency, such as internal bleeding from a ruptured tumour in the spleen. If you own a Bernese Mountain Dog, Golden Retriever, German Shepherd or Boxer, you have statistically heard this diagnosis more often among relatives than owners of other breeds. This article explains what haemangiosarcoma is, why it is so difficult to detect early, and which treatment options modern veterinary oncology offers.

What haemangiosarcoma is

HSA arises from endothelial cells. These are the cells that line the inner wall of blood vessels. Since these cells occur everywhere in the body, the tumour can grow in various places. The spleen is most frequently affected, followed by the right atrium of the heart, the liver and the skin. As it grows, HSA forms blood-filled cavities whose walls are thin and unstable. This is why the tumour tears easily and bleeds into the abdominal cavity or pericardial sac; often, internal bleeding is the first clinical sign that is noticed at all. Until then, the disease usually proceeds symptomlessly.

Added to this is a characteristic that makes HSA particularly aggressive: it metastasises early and readily. The lungs, liver, heart and spleen are the most common secondary sites; they are often already affected when the initial diagnosis is made.

Which dogs are particularly affected

Haemangiosarcomas account for 2 to 7 per cent of all dog tumours depending on the source, the range reflecting different study cohorts. For spleen tumours, the proportion is dramatically higher: around half of all malignant spleen tumours in dogs are haemangiosarcomas.

Typically for breeds, German Shepherds, Golden Retrievers, Labrador Retrievers, Boxers, Pointers and Bernese Mountain Dogs are significantly overrepresented. In the Bernese Mountain Dog, HSA adds to an already very high overall cancer burden; the breed has one of the lowest life expectancies in the middle field of the dog world, with a dominant tumour load. In the Golden Retriever, HSA is one of the most common forms of cancer alongside lymphoma and mast cell tumour, with particularly high mortality.

The special form cutaneous haemangiosarcoma (tumour in the skin) differs prognostically significantly from visceral (internal) HSA. Skin forms that arise due to UV radiation on sun-exposed, thin-skinned areas – abdomen, inner thighs, ears – are often limited to the skin and have significantly better healing prospects than internal forms.

Symptoms and diagnosis

The insidious thing about visceral haemangiosarcoma is the lack of symptoms. The dog appears normal for a long time. If something is noticed, it is often only through acute bleeding: sudden weakness, pale mucous membranes, accelerated breathing, collapse-like episodes. At this stage, it is already an emergency; internal bleeding can become life-threatening.

Diagnosis usually occurs in an emergency context: ultrasound of the abdominal cavity shows an enlarged spleen with masses, free fluid indicates that bleeding has already occurred. A definitive diagnosis requires pathological examination of the tissue, usually after removal of the spleen or other affected structures. If heart involvement is suspected, a cardiac ultrasound is added; the right atrium is one of the most common cardiac localisations.

For some at-risk breeds, veterinary oncologists recommend regular ultrasound screening from the seventh to eighth year of life. Although this does not reliably detect HSA in early stages – the tumours grow quickly and can develop between two annual examinations – it can identify individual cases earlier, thus opening the time window for an elective (planned) rather than an emergency operation.

Treatment: What is possible, and what is not

The standard treatment for HSA is surgical: removal of the tumour, usually with the entire affected organ. For spleen HSA, this means splenectomy (removal of the spleen). The median survival time after surgery alone is 1 to 3 months; the micrometastases that are usually already present at diagnosis are not addressed by the operation.

A combination of surgery and chemotherapy extends the median survival time. The classic protocol is doxorubicin-based; in the original study by Ogilvie et al. (1996) and several follow-up studies, dogs that underwent surgery plus doxorubicin achieved a median survival time of 4 to 6 months, some longer. This represents an extension of life, not a cure; most animals die from the tumour or its metastases, often within a year of diagnosis.

Newer approaches are being researched. The tyrosine kinase inhibitor Toceranib (Palladia®) is being investigated as maintenance therapy following doxorubicin protocols (Gardner et al. 2015, BMC Vet Res), with mixed results depending on the study context. Immunotherapy and gene therapy approaches are in preclinical studies but, as of 2025/2026, are not yet in widespread clinical use.

What you can take away as an owner

If your dog belongs to a high-risk breed, it helps to know three things. First: the disease progresses for a long time without symptoms; routine ultrasound from the seventh/eighth year of life is an option, not a guarantee. Second: acute weakness, pale mucous membranes and collapse-like episodes in a middle-aged or older dog constitute an emergency, not a case for observation. Go to the veterinary clinic immediately, do not wait for regular consultation hours. Third: once the diagnosis is confirmed, honest counselling regarding realistic prognoses and quality of life is more important than attempting to exhaust every possible therapy. Veterinary oncologists can concretely weigh both aspects, life extension and quality of life, and make the decision together with you.

With cutaneous haemangiosarcoma, particularly in light-skinned dogs with thin abdominal skin, regular skin checks are worthwhile. Altered, dark-red to bluish nodules or spots that grow quickly or bleed require veterinary investigation. Here, the prognosis for cure is significantly better with early removal than with internal forms.