Hemangiosarcoma (HSA) of the dog's spleen is a highly metastatic cancer that affects pets of any age. Even though it is most commonly seen in senior dogs (approx. 10 years old), there is no clear evidence that spleen tumors can only affect older animals (1).

This is a malignant vascular neoplasm that affects the dog's blood vessels and spreads to organs such as the liver, heart, lungs, muscles, skin, brain, and spinal cord. It has been estimated that spleen tumor in dogs makes up approximately 5% to 7% of all tumors occurring in the canine population (2).

What Is Splenic Hemangiosarcoma in Dogs?

Statistically, approximately 60% of bleeding tumors of the spleen in dogs are due to malignant hemangiosarcoma (3, 4). The remaining 40% are benign hemangiomas. They appear in the three most common types, including:

  • Splenic HAS in 40% to 50% of cases
  • Heart-based type in 10% to 25% cases
  • Dermal and hypodermal cancer in 15% cases

About 2/3 of dogs having pathological growth in the spleen will develop cancer on this organ, and in 2/3 of those dogs, this will be HSA.

Since this type of cancer is highly aggressive, there's an 80% chance it will spread from the moment the primary tumor occurs to the time it is diagnosed.

Every dog breed can suffer spleen cancer, but the research shows that it most commonly affects German Shepherd Dogs (5, 6). Also, the results of the survey published by the GRCA (Golden Retriever Club of America) show that one in five Golden Retrievers has a chance to develop HSA in their lifetime.

Other breeds that are susceptible to canine hemangiosarcoma include (7, 8):

  • German Shepherd Dogs (highest risk)
  • Boxers (highest risk)
  • Basset Hounds (highest risk)
  • St. Bernards (highest risk)
  • Scottish Terriers
  • Bulldogs
  • Airedales
  • Weimaraners
  • Golden Retrievers
  • Doberman Pinschers
  • Labrador Retrievers
  • English Setters
  • Great Danes

The dermal and hypodermal forms of dog spleen tumors are more typical for breeds like Whippets, Dalmatians, and Basset Hounds.

Mixed breeds, Miniature and Toy Poodles, Pomeranians, Chihuahuas, Boston Terriers, Cocker Spaniels, and Dachshunds, are at the lowest risk of spleen tumors (9, 10). However, recent reports from surveys are warning that the prevalence risk might be changing, though we still have no studies with precise numbers (11).

Causes of Spleen Tumor in Dogs

Even though the first reports of canine HSA go back as far as the 1960s, the exact cause of the spleen tumor in dogs is still unknown (12, 13, 14).

The most likely cause of canine hemangiosarcoma is genetic predisposition, which was observed in studies to be likely responsible for the occurrence of this disease, and it almost always occurs in certain dog breeds (15, 16).

It is also possible that the combination of heritable risk factors and the environment may cause mutations in the dog, which consequently results in HSA. For example, studies show that dogs exposed to ionizing radiation will develop spleen tumors (17, 18, 19). Other studies also showed a correlation between HSA and Leishmaniasis (20).

Symptoms of Hemangiosarcoma in Dogs

Unfortunately, the first symptoms of HSA appear when the disease has already advanced, even though the growth of dog hemangiosarcoma is generally slow (21). As the disease progresses, the dog (often a senior pet) will quit eating and will become lethargic. Consequently, the following signs can be noticed (22, 23):

  • Lack of appetite and weight loss
  • Partial loss of muscle control and ataxia
  • Confusion, seizures, and dementia
  • Excessive bruising
  • Pale gums
  • Palpable abdominal mass

Sometimes, clinical signs occur suddenly as a result of the rupture of the tumor in the spleen and significant internal bleeding. They include:

  • Acute weakness and inability to walk (lameness)
  • Tachycardia (rapid heart rate)
  • Bloated abdomen
  • Collapse

Without adequate treatment, the dog dies within approximately 6 to 8 weeks after the first signs of cancer occur, depending on the location of the tumor. In most cases, acute blood loss is fatal for the animal.

Diagnosis of Dog Spleen Tumors

The dog's medical history may give a veterinarian some information about potentially affected organs (24). There is no highly precise blood screening test for this type of cancer in dogs, but splenic tumors are usually diagnosed through hematologic and imaging examinations (25, 26). Other tests will help in determining the final diagnosis:

  • Complete blood count
  • Biochemistry profile
  • Coagulation testing
  • Urinalysis
  • X-rays and Ultrasounds (for revealing masses in the spleen and liver)
  • Thoracic radiography (for detecting eventual metastasis in lungs)
  • EKG (for discovering fluid around the heart)
  • Tumor tissue biopsy (the most accurate method of diagnosing HSA)

Treatment of Spleen Tumors in Dogs

Once the dog's spleen tumor has been diagnosed, the primary method of treatment is surgery (27). Unlike cutaneous tumors, where it is enough to remove the locally affected tissue, the only way to stop the growth of splenic HSA is splenectomy (spleen removal).

Such surgery is very complex since the blood loss is incredibly high both before and during the procedure. Blood transfusions are necessary before and during the operation, but sometimes the dog needs blood even in the postoperative period.

Approximately a week after tumor removal, the dog will be lethargic and tired. The first signs of improvement will come within ten days. After two weeks, the vet will remove the sutures.

In some more rare cases, there are other forms of treatment, which are often combined with the surgery as a first option:

Chemotherapy. The vet will recommend this type of therapy after the operation to prevent possible metastases. The standard chemotherapy procedure in such a case includes intravenous doxorubicin every three weeks, which provides relief and alleviates the symptoms of the disease. Other combinations may include vincristine, methotrexate, and cyclophosphamide, but the results obtained are not satisfying.

Radiotherapy. Since the metastatic rate of this type of cancer is too high, this therapy is not widely used. However, further research may prove the purposefulness of this treatment in combination with chemotherapy in the future.

Immunotherapy. The treatment, which includes L-MTP-PE (liposome-encapsulated muramyl tripeptide-phosphatidylethanolamine), leads to an improvement in the overall condition. Currently, this approach is not available in the US.

Spleen tumor surgery comes with side effects, too. Studies found that dogs, after surgery, are very likely to demonstrate intolerance to exercise, insufficient response to reduced cardiac output, decreased response to hypoxia, and susceptibility to erythrocyte parasitism (28, 29).

Prognosis for a Dog with a Spleen Tumor

Visceral canine hemangiosarcoma is far more common than cutaneous canine hemangiosarcoma, and dogs suffering from the former sadly have a lower chance of survival (30).

Unfortunately, the overall prognosis is not good for dogs with spleen tumors, even when combined splenectomy and chemotherapy are performed. After surgical intervention, the median survival time for most dogs is from 75 to 86 days, depending on the stage of cancer (31, 32, 33).

A year after surgery, only 6% to 13% of dogs will survive (34). The survival chance will increase when the surgery is combined with chemotherapy. In that case, the survival rate within the first year can be anywhere from 12% to 20%.

Dogs with anemia have a much lower chance of survival (35). Dogs with the presence of blood in their peritoneal cavity (a condition known as hemoperitoneum) also have a lower survival chance of spleen tumor surgery (36).

Prevention of Spleen Tumors

The only way to prevent hemangiosarcoma is by tracking bloodlines since a heritable factor is probably the crucial cause of its appearance. Knowing the breed's history and chances of such diseases through dog DNA testing can be beneficial for dog owners.

The proof is the fact that almost 61.4% of Golden Retrievers in the US die from neoplasia.  On the other hand, cancer is a reason for the death of just 38.8% of Goldens from English bloodlines.

Oncologists note that breeds predisposed to splenic HSA may benefit from ultrasounds once a year after they turn five years old. Also, taking the dog to the vet once every six months for palpation of the abdomen may help detect the disease on time, which increases survival chances.

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Kelly works as a veterinary technician in Austin, TX as well as regular animal rescue volunteer. She's been an animal lover and dog owner since childhood, and has worked in different dog related fields over the last twenty years. Currently she lives with three dogs and a cat.