CONDITION

Hemangiosarcoma

Why this matters now

Hemangiosarcoma is an aggressive cancer arising from blood vessel cells, most commonly affecting the spleen, heart, or liver in dogs. German Shepherds and Golden Retrievers are particularly predisposed, though any breed can be affected. The tumour often grows silently within internal organs, causing few signs until it bleeds or ruptures. This means diagnosis frequently occurs during a crisis—sudden collapse from internal bleeding—rather than during routine care.

Hemangiosarcoma typically develops as blood-filled masses that grow within organs. These tumours are fragile and prone to rupture, causing acute internal bleeding. Episodes of bleeding may be small and self-limiting initially, causing vague symptoms, before a larger bleed causes collapse. The cancer spreads readily to other organs, particularly the liver, lungs, and heart. Even with treatment, the prognosis is guarded due to the high metastatic rate.

Signals & patterns

Early signals

Episodes of weakness or collapse that resolve

Small bleeds may cause transient weakness followed by apparent recovery as the body reabsorbs the blood.

Lethargy and reduced stamina

Vague tiredness that may be attributed to age can reflect chronic low-grade blood loss.

Pale gums

Anaemia from blood loss causes visible pallor of the mucous membranes.

Distended abdomen

Free blood or an enlarged spleen may cause abdominal swelling.

Later signals

Sudden collapse

Acute haemorrhage causes rapid deterioration, weakness, and inability to stand.

Rapid, weak pulse

Shock from blood loss causes cardiovascular signs.

Breathing difficulty

Pericardial effusion (blood around the heart) causes respiratory distress. Lung metastases may also affect breathing.

Irregular heart rhythm

Cardiac involvement can cause arrhythmias.

Click to read about the biological mechanisms

How this is usually investigated

Investigation often occurs during an emergency presentation but may also follow incidental findings. Staging assesses the extent of disease.

Abdominal ultrasound

Purpose: To visualise the spleen, liver, and look for masses or free fluid
Considerations: Can identify splenic masses and assess for bleeding. Multiple masses or liver involvement may suggest advanced disease.

Chest radiographs

Purpose: To look for lung metastases and assess heart size
Considerations: Visible lung nodules indicate spread. Enlarged cardiac silhouette may suggest pericardial effusion.

Echocardiography

Purpose: To examine the heart for tumours or pericardial effusion
Considerations: Identifies cardiac masses and guides pericardiocentesis if effusion is present.

Blood tests

Purpose: To assess anaemia and organ function
Considerations: Packed cell volume indicates degree of blood loss. Clotting tests may be abnormal.

Histopathology

Purpose: To confirm the diagnosis after surgical removal
Considerations: Definitive diagnosis requires microscopic examination of tissue. Not all splenic masses are hemangiosarcoma—some are benign.

Options & trade-offs

Treatment decisions depend on tumour location, extent of disease, and the dog's overall condition. Options range from emergency stabilisation to planned surgery and chemotherapy.

Emergency stabilisation

Intravenous fluids, blood transfusion, and supportive care for dogs presenting in crisis.

Trade-offs: May be lifesaving in the short term. Provides time for diagnostic evaluation and decision-making. Some dogs stabilise well enough for surgery.

Splenectomy

Surgical removal of the spleen when it contains the primary tumour.

Trade-offs: Stops active bleeding. Dogs can live normally without a spleen. Provides tissue for diagnosis. Survival after surgery alone averages one to two months due to metastatic disease.

Surgery with chemotherapy

Combining splenectomy with systemic chemotherapy to address micrometastases.

Trade-offs: Extends median survival to four to six months, with some dogs living longer. Chemotherapy is generally well tolerated.

Pericardiocentesis

Draining blood from around the heart to relieve tamponade.

Trade-offs: Can be lifesaving in cardiac hemangiosarcoma. May need repeating. Provides temporary relief but does not treat the underlying tumour.

Palliative care

Supportive treatment focused on comfort when curative options are not pursued.

Trade-offs: Appropriate for advanced disease or when other treatments are declined. Focuses on quality of remaining time.

Common misconceptions

Misconception:

"A mass on the spleen means cancer"

Reality:

Approximately two-thirds of splenic masses in dogs are malignant (hemangiosarcoma or other cancers), but one-third are benign. Definitive diagnosis requires histopathology after removal.

Misconception:

"Removing the spleen cures hemangiosarcoma"

Reality:

Surgery removes the primary tumour but microscopic spread has usually already occurred. Chemotherapy helps extend survival but cure is rare.

Misconception:

"There were no warning signs, so nothing could have been done earlier"

Reality:

Hemangiosarcoma often causes no obvious signs until rupture. This reflects the nature of the disease rather than missed opportunities. Some dogs do have subtle signs that, in retrospect, may have been related.

Understanding that splenic masses require investigation regardless of whether they cause symptoms helps with incidental findings. Being aware that at-risk breeds may benefit from periodic abdominal ultrasound screening is worth discussing. Recognising signs of internal bleeding—weakness, pale gums, distended abdomen—enables prompt action. Knowing that prognosis depends on tumour type helps frame expectations whilst awaiting histopathology.

Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS