Spleen Cancer in Dogs

By Lauren Jones, VMD on Apr. 28, 2022

A domestic dog is examining in a veterinary clinic.

What is Spleen Cancer in Dogs?

In dogs, the spleen plays a role in the immune system, helping the body fight off infection and produce certain types of white blood cells. It also stores and produces new red blood cells and removes old red blood cells. At any given time, the spleen stores up to 20% of all the red blood cells and 30% of platelets in the body.

The spleen is oblong shaped and located in the abdomen, below the stomach. While the spleen does play a role in keeping animals healthy, it is not a vital organ and can be removed with few long-lasting effects.

Splenic tumors are very common in dogs, especially as they grow older. Because the spleen stores and produces red blood cells, even benign tumors may be at risk of rupture and bleeding, causing acute illness.

Veterinarians class tumors as:

Benign (non-cancerous)
Malignant (cancerous)
Primary (originated in the spleen) or secondary (spread from another tumor somewhere else)
Focal (located in one area) or diffuse (spread throughout the entire organ)

Hemangioma and hemangiosarcoma are two of the most common primary tumors found in spleens. Hemangiomas are benign, while hemangiosarcomas are malignant. The prognosis for any specific spleen tumor depends on the type of tumor. Benign tumors, which may still require treatment and removal, carry a better prognosis, or outcome, overall than malignant tumors, especially if treated early.

Any dog can develop tumors in their spleen, but older, larger breed dogs are at higher risk. Breeds most at risk include:

German Shepherd
Golden Retriever
Labrador Retriever
Boxer
Standard Poodle
Bernese Mountain dog
Flat-Coated Retriever

Benign Spleen Tumors

Benign spleen tumors are non-cancerous but are easy to confuse with malignant tumors. When veterinarians find any tumor on the spleen, they may recommend additional tests to rule out more sinister diseases. Benign tumors do not spread to other parts of the body and do not pose a risk of metastasis. Many benign tumors may still be removed and can have a good prognosis, if they are caught early.

Malignant Spleen Tumors

While the prognosis for benign tumors is typically good if discovered early, the same is not true for malignant tumors. The outcome for malignant tumors varies based on how aggressive the cancer is. Common malignant tumors in the spleen include:

Lymphoma or lymphosarcoma: This is a highly variable type of round cell tumor that typically involves the lymph nodes as well as other organs. Lymphoma is typically aggressive with a poor prognosis.
Leukemia: Leukemia is typically a cancer of cells within the bone marrow, but can originate in or infiltrate the spleen. Canine leukemia is rare, but typically carries a poor prognosis with splenic involvement.
Other round cell tumors include mast cell tumors, plasma cell tumors, and multiple myeloma. Prognosis varies with severity and metastasis but is generally guarded.
Histiocytic sarcoma: This type of sarcoma is very common in Bernese Mountain Dogs, as well as other breeds. Prognosis is very poor to grave in most cases of histiocytic sarcoma.
As with all other types of splenic neoplasia, the type, aggressiveness, and location determine prognosis. There are many other less common types of malignant splenic tumors, mostly all carrying a similar poor prognosis, including:
- Leiomyosarcoma
- Melanoma
- Carcinoma

Secondary tumors are also common in the spleen. These are caused by cancerous spread from other sites in the body. Because the spleen is very vascular, meaning it has a rich blood supply, it’s a common site for secondary tumors.

Symptoms of Spleen Cancer in Dogs

Signs of splenic tumors in dogs can be vague or even nonexistent, and they are often found during a diagnostic test for other conditions. A major concern of most tumors in the spleen is rupture. Because the spleen contains many blood vessels, even benign tumors have the potential to break open and cause either a slow or fast bleed. Slow bleeds will show more mild signs, while a fast bleed can result in an acute, severe, life-threatening blood loss into the abdomen.

Common signs of a spleen tumor or bleeding include:

Lethargy
Decreased appetite
Weakness
Collapse
Pale gums
Abdominal enlargement (such as bloating or swollen abdomen)
Cold limbs
Heart arrhythmia

Causes of Spleen Cancer in Dogs

The cause of most splenic tumors is unknown. German Shepherds, Labrador Retrievers, Golden Retrievers, Boxers, and Standard Poodles may have a higher risk of splenic tumors in general. Bernese Mountain Dogs and Flat-Coated Retrievers may have a genetic link to histiocytic sarcoma. Splenic cancer can occur in all ages of dogs, but veterinarians most often diagnose in older dogs.

How Veterinarians Diagnose Spleen Cancer in Dogs

Veterinarians may suspect a bleeding splenic tumor based on clinical signs and physical exam alone. Large enough tumors can be felt (palpated) through the abdominal walls, and a fluid wave in the abdomen from bleeding is frequently present as well.

Blood chemistry and complete blood count (CBC)

Veterinarians will often recommend bloodwork as a first step to determine overall health after diagnosing a splenic tumor. A bleeding or ruptured tumor will often lead to anemia (low red blood cell count) and low platelets, which can be detected by a complete blood count. The blood chemistry panel may show issues common to many conditions, such as dehydration.

Coagulation Tests

Because low platelets and other factors necessary for clotting are common signs in some types of splenic tumors, coagulation tests will be done to determine if a dog is at risk for severe bleeding issues. This type of test (which includes prothrombin and partial thromboplastin times) measures how long it takes the blood to clot. Abnormal results could indicate the disease is more advanced and the patient is at risk for further bleeding. Coagulation tests may be performed if bleeding is suspected and can help guide treatment, such as blood product transfusions, that could increase survival during surgery.

Radiography

Radiographs, or x-rays, are useful to determine the overall size, shape, and placement of the spleen in reference to other abdominal organs. Veterinarians may note obvious masses in the spleen, or it may be generally enlarged and abnormally shaped. Veterinarians will also want to take x-rays of the lungs to look for cancerous spread.

Ultrasonography

Ultrasonography allows more detailed analysis of the internal structure, location, and size of the spleen and other abdominal organs. Veterinarians will also use ultrasound as a guide when they obtain biopsies, which is one way to get a definitive diagnosis. Veterinary radiologists evaluate the entire abdominal cavity for other tumors, abnormalities, and fluid.

Fluid analysis and cytology

Dogs with a ruptured splenic tumor commonly have abnormal fluid accumulation in the abdomen. Typically, this fluid is blood, and vets can easily obtain a sample by directing a needle into the abdominal fluid. Vets may analyze this fluid using a microscope to assess for cancerous cells. This method may be more helpful in diagnosing lymphoma and mast cell tumors but isn’t accurate in all cases.

Biopsy

Splenic biopsy can be performed under ultrasound guidance with a large needle to collect a sample of spleen cells, as well as during surgical removal of the spleen.

Treatment of Spleen Cancer in Dogs

Surgery

Regardless of whether a splenic tumor is malignant, removal of the spleen, called a splenectomy, is most often recommended as treatment for primary splenic tumors because even benign tumors can rupture and cause life-threatening illness.

The surgery is relatively simple, and may not require a veterinary specialist to perform, as many general practitioners are comfortable. The spleen is not a vital organ, and therefore vets remove the entire spleen, not just the tumor.

Before surgery, a complete work-up should be performed to look at overall health and cancer spread, called cancer staging. This may include bloodwork, x-rays of the chest and ultrasound of the abdomen. Based on the findings of these tests, vets will determine if a patient is a good surgical candidate for splenectomy.

In the cases of advanced disease, cancerous spread, or poor surgical candidacy, surgery may not be recommended. However, there are cases of malignant tumors that may still benefit from a splenectomy.

Chemotherapy

Veterinary oncologists typically recommend chemotherapy after removal of splenic tumors, based on the specific tumor type. In some cases, depending on the type of tumor, chemotherapy is not necessary.

Medications

Medications are typically not a primary recommendation for dogs with splenic tumors. However, if a patient is not a candidate for surgery, medication may improve their quality of life. Dogs who do not have the spleen removed are still at risk of splenic rupture, and many vets utilize the Chinese herbal supplement Yunnan Baiyao to help control bleeding.

Other medications, such as steroids, are prescribed in some types of cancer. Unfortunately, these medications do not cure anything and only make the dog’s quality of life better for a short period of time.

Prognosis of Spleen Cancer in Dogs

Prognosis of splenic cancer varies based on diagnosis. When caught early, benign tumors, most notably hematomas and other vascular tumors, may only require a splenectomy to prevent a rupture and hemorrhage. If the tumor was found coincidentally, and the pet is not actively sick, the prognosis may be excellent with full life expectancy.

Patients who have concurrent illnesses, or if benign tumors chronically or acutely rupture, can also have clotting and anemia issues and may have a more guarded prognosis.

Malignant tumors carry a more guarded to grave prognosis. Many dogs are not stable enough to undergo anesthesia due to the changes in blood and coagulation factors. Because of this, many dogs undergoing an emergency splenectomy pass away or are euthanized during surgery.

Survival times after a splenectomy range from less than month to up to three months for dogs with splenic hemangiosarcoma (one of the most severe malignant tumors). Dogs treated with a splenectomy and chemotherapy may have a longer survival time depending on their individual case. However, there are many complicating factors involving specific diagnosis, stage, and metastatic rates.

Dogs who receive no treatment of malignant, bleeding splenic tumors have an extremely dire prognosis. Tumors can bleed slowly, with the dog showing varying signs of illness and weakness. Tumors can also rupture acutely and traumatically. These dogs are critically sick, weak, and can die from loss of blood. These patients should be immediately evaluated by a veterinarian to determine if surgery is still an option or if humane euthanasia is the best choice.

Recovery and Management of Spleen Cancer in Dogs

Dogs with their spleen removed require normal postoperative care including incisional monitoring and routine pain management. They will likely have an incision from the sternum down to the pelvis. These patients should have decreased activity and incision monitoring for at least 10-14 days.

All splenic tumors should be biopsied for a definitive diagnosis. Surgery may be curative for benign tumors with no other illnesses or complications.

For those patients with more advanced disease, rechecks with surgeons and oncologists may be scheduled initially at 2 weeks, and then every 1-3 months depending on the plan going forward. The veterinarians will likely check bloodwork parameters, x-rays, and ultrasounds at these visits to monitor disease progression and quality of life.

Based on the severity of the disease, some complications may require more intensive care and monitoring such as: