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Hemangiosarcoma in dogs: spleen mass and blood work

Hemangiosarcoma is a malignant tumour that grows most often in the spleen, the heart or the liver. It can bleed inside the body without warning. Blood tests cannot name it, but anemia, low platelets and clotting changes are strong clues, and they help your vet decide what to do next.

Written by the AI DiagAnimals editorial teamReviewed by the AI DiagAnimals TeamUpdated Our editorial policy

The essentials

Hemangiosarcoma (HSA) most often starts in the spleen, then the right atrium of the heart and the liver. Many dogs are brought in for weakness or pale gums after bleeding into the belly. The blood count often shows anemia and low platelets, the most common abnormality; clotting tests can show DIC. Not every spleen mass is cancer: masses found by chance are benign in about 70% of cases. Only the lab exam of the removed tissue gives the final answer.

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What hemangiosarcoma is and where it grows

Hemangiosarcoma (HSA) is a malignant tumour of blood-vessel origin. In dogs its main primary sites are, in order, the spleen, the right atrium of the heart and the liver [1]. Visceral HSA (inside the body) makes up under 2% of canine biopsy submissions; skin and other non-visceral forms under 1% [3].

German Shepherds are over-represented [1, 4]. In the Golden Retriever Lifetime Study, 7.65% of 3,044 dogs were diagnosed with HSA, most of them with the visceral form [2]. Italian Greyhounds, Greyhounds and Whippets are over-represented for the skin form [3].

Signs are often vague and come and go: episodes of lethargy and weakness, depression, poor appetite and pale gums [4].

What the blood count and clotting tests show

Most figures come from small studies (9 to 37 dogs). A normal blood count does not rule HSA out.
TestWhat is often foundWhat it means
Red cells (HCT, PCV)Anemia in 97% of dogs with non-traumatic bleeding into the belly [5]; usually mild to moderate [4]Blood loss, often internal. See anemia in dogs.
Platelets (PLT)Low in 75% of dogs, the most common abnormality [6]; lower with HSA than with other spleen masses [7, 8]Consumption by the tumour and bleeding. See low platelets in dogs.
Red cell shapes on the smearAcanthocytes in 90%, schistocytes in 80%, keratocytes and nucleated red cells in 70% of 9 dogs [4]Suggestive, but not specific: only 12 of 123 dogs with acanthocytes had HSA [9].
Clotting tests (PT, aPTT, fibrinogen, FDP)DIC in 50% at diagnosis [6]; a clotting disorder in 84% of dogs with bleeding into the belly [5]Disseminated intravascular coagulation, a dangerous clotting imbalance [11].
AlbuminLow in 76% of dogs with bleeding into the belly [5]Protein lost with the blood. See albumin and globulin in dogs.

In dogs with HSA, acanthocytes are frequently accompanied by schistocytes and low platelets, and such dogs often have laboratory signs of DIC [10]. Fragmented red cells are seen in only about 20% of dogs with DIC, so their absence does not rule DIC out [11]. Read the full CBC for dogs guide for each value.

Low platelets: the most common clue

In a study of 24 dogs with HSA, a low platelet count was present in 75% and was the most common abnormality; the mean count was 137,800/µL. Half of the dogs had DIC at presentation, and 25% died of these clotting problems [6]. Lower platelets and lower red cell values are more frequent with HSA than with other causes of a spleen mass or of bleeding into the belly [7, 8].

An annotated line from a lab report · Illustrative example
AbbreviationResultUnitLaboratory intervalFlag
PLT Platelets62× 10³/µL148–484L
  1. Abbreviation PLT: platelet count, part of the complete blood count.
  2. Result 62 × 10³/µL (62,000/µL) in this illustrative line: clearly low.
  3. Unit × 10³/µL, also written K/µL; × 10⁹/L gives the same number.
  4. Laboratory interval An illustrative dog interval; each laboratory sets its own.
  5. Flag L: below the interval. With anemia and a spleen mass, vets check clotting tests for DIC [6]. See low platelets in dogs.

A spleen mass: the “double two-thirds rule” and newer numbers

An old rule of thumb says that about two-thirds of spleen masses are malignant, and about two-thirds of those are HSA. Recent studies refine it. In 288 dogs with a spleen mass, 60% had a malignant tumour, and HSA made up 66% of these; the breed group and bleeding into the belly helped predict HSA [13]. An earlier study found a primary malignant tumour in 59 of 100 dogs, with HSA in 43 [12].

Context matters. When the mass was found by chance and had not ruptured, 70.5% of 105 masses were benign; HSA accounted for 18 of the 31 malignant ones [14]. In anemic dogs with bleeding into the belly that needed a transfusion, 76.1% had a malignant tumour and 70.4% had HSA [7]. Benign hematomas are common and can look exactly like HSA to the naked eye [17].

How hemangiosarcoma is diagnosed

  • Blood count, chemistry and clotting tests: they show anemia, low platelets and DIC [5, 6]. Nucleated red cells, anemia, abnormal red cell shapes or a ruptured spleen made a spleen tumour more likely in one study [12].
  • Abdominal imaging: shows the mass and any blood in the belly. Bleeding into the belly made HSA more likely in a study of 288 dogs [13].
  • Heart ultrasound (echocardiography): looks for a mass in the right atrium; a mass presumed to be HSA was confirmed in 4 of 8 dogs [15].
  • Histopathology: because hematoma and HSA can look the same [17], the diagnosis is confirmed by the laboratory exam of the removed tissue.

Outlook

The outlook for the visceral form is poor. In 208 dogs with spleen HSA treated by surgery alone, median survival was 1.6 months; the stage of the disease was the only significant prognostic factor, and added chemotherapy gave modest gains in the first months [16]. With HSA found by chance in a non-ruptured mass, median life expectancy was 132 days [14]. When HSA caused fluid around the heart, median survival was 16 days [18].

Skin HSA does much better: 84.6% of Golden Retrievers with the skin form were alive at one year, against 1.42% with the visceral form [2]. Complete removal is the most important factor [3].

Related articles

See also mast cell tumors in dogs and immune thrombocytopenia (ITP), another cause of very low platelets. En français : hémangiosarcome du chien.

Questions to ask your veterinarian

  1. Is my dog anemic, and is the anemia from bleeding?
  2. Are the platelets low, and do the clotting tests suggest DIC?
  3. Is there fluid in the belly or around the heart?
  4. Could this spleen mass be benign, such as a hematoma?
  5. Will the removed tissue be sent for histopathology?
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Frequently asked questions

What is the 2/3 2/3 rule for hemangiosarcoma?

A rule of thumb: about two-thirds of spleen masses are malignant, and about two-thirds of those are HSA. In a 2020 study of 288 dogs, 60% of masses were malignant and HSA made up 66% of these [13]. Masses found by chance are more often benign (70.5%) [14].

What is canine hemangiosarcoma (HSA)?

A malignant tumour of blood-vessel origin. In dogs it starts mostly in the spleen, the right atrium of the heart and the liver [1]; a skin form also exists [3].

What are the symptoms of a dog spleen tumor?

Episodes of weakness and lethargy, depression, poor appetite and pale gums [4]. A mass that bleeds into the belly causes anemia [5]. Some masses cause no signs: 28% were found by chance in one study [13].

What are the early signs of hemangiosarcoma in dogs?

They are often vague and come and go, like short spells of tiredness or weakness [4]. A blood count may already show anemia or low platelets [4, 6].

How long do dogs typically live with hemangiosarcoma?

For spleen HSA treated by surgery alone, median survival was 1.6 months in 208 dogs [16]. The skin form has a much better outlook [2].

Sources

  1. Hirsch VM, Jacobsen J, Mills JH. A retrospective study of canine hemangiosarcoma and its association with acanthocytosis. Can Vet J. 1981;22(5):152-5. pubmed.ncbi.nlm.nih.gov/7195770
  2. Hillman A et al. Descriptive analysis of haemangiosarcoma occurrence in dogs enrolled in the Golden Retriever lifetime study. Vet Comp Oncol. 2023;21(4):700-708. doi.org/10.1111/vco.12933
  3. Schultheiss PC. A retrospective study of visceral and nonvisceral hemangiosarcoma and hemangiomas in domestic animals. J Vet Diagn Invest. 2004;16(6):522-6. doi.org/10.1177/104063870401600606
  4. Ng CY, Mills JN. Clinical and haematological features of haemangiosarcoma in dogs. Aust Vet J. 1985;62(1):1-4. doi.org/10.1111/j.1751-0813.1985.tb06029.x
  5. Pintar J et al. Acute nontraumatic hemoabdomen in the dog: a retrospective analysis of 39 cases (1987-2001). J Am Anim Hosp Assoc. 2003;39(6):518-22. doi.org/10.5326/0390518
  6. Hammer AS et al. Hemostatic abnormalities in dogs with hemangiosarcoma. J Vet Intern Med. 1991;5(1):11-4. doi.org/10.1111/j.1939-1676.1991.tb00923.x
  7. Hammond TN, Pesillo-Crosby SA. Prevalence of hemangiosarcoma in anemic dogs with a splenic mass and hemoperitoneum requiring a transfusion: 71 cases (2003-2005). J Am Vet Med Assoc. 2008;232(4):553-8. doi.org/10.2460/javma.232.4.553
  8. Wong RW et al. Erythrocyte and biochemical abnormalities as diagnostic markers in dogs with hemangiosarcoma related hemoabdomen. Vet Surg. 2015;44(7):852-7. doi.org/10.1111/vsu.12361
  9. Warry E et al. Disease distribution in canine patients with acanthocytosis: 123 cases. Vet Clin Pathol. 2013;42(4):465-70. doi.org/10.1111/vcp.12097
  10. eClinPath, Cornell University College of Veterinary Medicine. Poikilocytosis. eclinpath.com/hematology/morphologic-features/red-blood-cells/poikilocytosis
  11. eClinPath, Cornell University College of Veterinary Medicine. Disseminated intravascular coagulation. eclinpath.com/hemostasis/disorders/dic
  12. Johnson KA et al. Splenomegaly in dogs: predictors of neoplasia and survival after splenectomy. J Vet Intern Med. 1989;3(3):160-6. doi.org/10.1111/j.1939-1676.1989.tb03092.x
  13. Davies O, Taylor AJ. Refining the “double two-thirds” rule: genotype-based breed grouping and clinical presentation help predict the diagnosis of canine splenic mass lesions in 288 dogs. Vet Comp Oncol. 2020;18(4):548-558. doi.org/10.1111/vco.12574
  14. Cleveland MJ, Casale S. Incidence of malignancy and outcomes for dogs undergoing splenectomy for incidentally detected nonruptured splenic nodules or masses: 105 cases (2009-2013). J Am Vet Med Assoc. 2016;248(11):1267-73. doi.org/10.2460/javma.248.11.1267
  15. Rajagopalan V et al. Comparison of presumptive echocardiographic and definitive diagnoses of cardiac tumors in dogs. J Vet Intern Med. 2013;27(5):1092-6. doi.org/10.1111/jvim.12134
  16. Wendelburg KM et al. Survival time of dogs with splenic hemangiosarcoma treated by splenectomy with or without adjuvant chemotherapy: 208 cases (2001-2012). J Am Vet Med Assoc. 2015;247(4):393-403. doi.org/10.2460/javma.247.4.393
  17. Spangler WL, Culbertson MR. Prevalence, type, and importance of splenic diseases in dogs: 1,480 cases (1985-1989). J Am Vet Med Assoc. 1992;200(6):829-34. pubmed.ncbi.nlm.nih.gov/1568933
  18. Dunning D et al. Analysis of prognostic indicators for dogs with pericardial effusion: 46 cases (1985-1996). J Am Vet Med Assoc. 1998;212(8):1276-80. pubmed.ncbi.nlm.nih.gov/9569169

Laboratory methods and reference intervals vary. This article explains; it does not diagnose. For a decision about your pet, use the original report and talk to your veterinarian. Our editorial policy.

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