Spleen Cancer in Dogs

Though spleen cancer in dogs is, thankfully, relatively rare, it is one of the more common types of cancer veterinarians see in their canine patients. Spleen cancer tends to happen in older, large-breed dogs, and it can be life-threatening. 

As a pet parent, hearing a diagnosis of dog spleen cancer can be extremely stressful. That’s why I’m going to explain everything you need to know about spleen cancer, so you can make the best decisions for your pet.

What is Spleen Cancer in Dogs?

The spleen is an organ in your dog’s abdomen. It stores blood, filters blood cells, and helps promote immune response by making and storing lymphocytes. Though it does an important job, the spleen is not an essential organ; it is possible to survive without a spleen. 

Cancer is when cells grow or replicate uncontrollably. When these cells form tumors that spread and interfere with normal bodily function, they are classified as malignant. Tumors that form but do not spread or metastasize are benign.  

In canine spleen cancers, it’s typically the cells lining blood vessels that replicate abnormally. These tumors can grow large and eventually pop, causing internal bleeding.

Spleen cancer can be especially dangerous because it doesn’t cause many symptoms at first. So the disease often goes undetected until it’s quite advanced. 

Sometimes, vets discover splenic cancer in dogs when investigating other health concerns. The first case of spleen cancer I diagnosed was in an eight-year-old female (spayed) chocolate Labrador Retriever. I determined the dog’s mild anemia was due to a slowly bleeding spleen tumor. In more serious cases, dogs with spleen cancer may collapse due to severe internal bleeding and require emergency surgery.

Types of Spleen Cancer in Dogs

There are several types of spleen cancer in dogs, each named for the cell type affected.  

Splenic hemangiosarcoma is the most common spleen cancer in dogs. It is a malignant cancer of the blood vessels found in about half the cases of spleen cancer in dogs. 

Vets often cite the “double two-thirds rule” when talking about the risk of this type of spleen cancer. This so-called rule estimates that roughly two-thirds of spleen cancers will be malignant, and two-thirds of those will be hemangiosarcoma. (1)

A recent review suggests the likelihood could be even higher — with 70 percent of splenic tumors found to be malignant and 83 percent of malignancies found to be hemangiosarcoma. (2)

The balance of malignant spleen cancers in dogs may include lymphomas, histiocytic sarcomas, and osteosarcomas, among others.

Non-malignant tumors can include hematomas, abscesses, nodular hyperplasia, or benign hemangiomas.

Causes of Dog Spleen Cancer

Spleen cancer in dogs is just a random mutation in the cells making up the spleen. It has no cause as such, and there’s nothing you can do to predict or prevent spleen cancer from developing. Because splenic tumors are slightly more common in German Shepherds, Cocker Spaniels and Labrador Retrievers, there may be genetic risk factors at play. (3)  But more research is needed to determine what roles genes play in canine spleen cancer.

Symptoms of Spleen Cancer in Dogs

The symptoms of spleen cancer in dogs are often hard to detect. In the early stages, a veterinarian is more likely to discover a tumor while investigating other health issues or during a regular physical exam.

But as spleen cancer progresses, if tumors grow large enough or are damaged by a knock or a fall, they can burst, causing internal bleeding.  

While you may not be able to see the bleeding, you might notice related symptoms, including:

• Pale gums
• Low body temperature
• Reluctance to move, lethargy, or weakness
• Abdominal swelling
• Increased heart rate and fast breathing

These symptoms may suddenly improve if the bleeding stops on its own, but it will always start again at some point. 

Splenic tumors can be very fragile, and eventually, the spleen will be too damaged by the tumor to stop bleeding on its own. The more blood dogs lose at this point, the more risky surgery becomes. So it’s crucial to act quickly and visit your veterinarian if you suspect your dog might have spleen cancer.

Dog Spleen Cancer Stages and Progression

Spleen tumors start microscopically small and then gradually grow larger. In the earliest phase, there’s nothing obviously wrong with the spleen. Even if a vet were able to examine it visually, nothing would appear amiss. 

In the next phase, the spleen starts to change. However, since there are no other symptoms, its abnormal appearance often goes undetected…unless, by chance, your dog requires abdominal imaging or surgery for some other reason.

In the late stages of spleen cancer, tumors on the spleen often start bleeding. This generally means the tumor is fairly large. If it’s a malignant one, there’s a high chance that the tumor has spread at this point. 

As with most cancers, early detection and treatment will give your dog the best outcome. Ideally, you’d want to remove the tumor before it starts bleeding or spreading. The problem is that it’s hard to spot spleen cancer early as there are often no signs. 

Bringing your dog in for regular checkups as they get older may help to catch a tumor, but it’s not always possible for your vet to feel a tumor on a physical exam (depending on its size and location).

Diagnosing Hemangiosarcoma in Dogs

If you suspect your dog may have spleen cancer, or if you’re simply worried because your dog’s breed faces a greater risk, talk to your veterinarian about your concerns. Your vet can conduct a thorough exam to evaluate your dog’s condition.

First, your veterinarian will perform a physical exam, paying particular attention to gum color, heart rate, and feeling the abdomen. 

Blood tests are often a good idea. They can detect the presence of concurrent issues, like kidney disease in dogs, as well as conditions that may be caused by splenic tumors, like anemia. This is an important step, but it won’t get a diagnosis on its own. 

Generally, hemangiosarcoma and other dog spleen tumors are diagnosed with imaging. Ultrasound is a good option for the spleen itself, but X-rays can also be used to diagnose spleen cancer. It’s a good idea to X-ray the chest and ultrasound the heart, as malignant tumors may already have spread to these areas, making spleen removal pointless.

If the tumor has not spread, your veterinarian will need to send a sample of it to the lab for analysis to determine if it is malignant or benign. While sampling the tumor with a needle is possible, it could also cause the tumor to bust. Instead, it may be easier to remove the spleen and send a sample of the tumor to the lab afterward.

Canine Spleen Cancer Treatment Options

In all cases of spleen cancer, the recommended treatment is a splenectomy — the surgical removal of the entire spleen. This is because even benign masses are prone to bursting and causing life-threatening internal bleeding. Removing the spleen prevents this from happening and also allows the tumor to be sent to a laboratory for identification. 

Of course, splenectomy in dogs isn’t the only option. If the tumor isn’t actively bleeding, you may decide to leave it alone. But you need to be aware that, at some point, it will start bleeding, which makes surgery more risky. 

As mentioned earlier, more often than not, lab results will indicate that the spleen tumor is malignant. In these cases, chemotherapy may help improve the life expectancy in dogs with spleen cancer. However, this dog cancer treatment can be costly, and may not be appropriate for all dogs, depending on their age and other health concerns. In some cases, pet parents may decide not to treat their dog’s spleen cancer and, instead, euthanize their dog when they show signs of internal bleeding. It’s impossible to predict when this could happen, as it depends on how early the tumor is diagnosed.

Cost to Treat Spleen Cancer in Dogs

Spleen removal in dogs is a major abdominal surgery. It can be performed by many vets (you don’t necessarily need a specialist surgeon). However, it is one of the more complicated surgeries we see in general practice. This means that it can be expensive, and pet owners should expect to pay around $800 to $1,500 for the surgery alone. 

Depending on the stage of their disease and whether they’re actively bleeding, dogs may also need blood transfusions, extended hospitalization, and chemotherapy. This could increase the cost of treatment to $4,000 or $5,000. 

Costs can also vary depending on your area. Your veterinarian will be able to give you an estimate so you can plan financially for treating your dog’s spleen cancer.

Prognosis for Spleen Cancer in Dogs

For dogs lucky enough to have benign tumors (about 30 percent of dogs), if they survive surgery (which about 95 percent of dogs do), they can look forward to a good prognosis and normal life expectancy. Unfortunately, the prognosis for dogs that have a malignant tumor is less promising. One study of over 200 dogs found that, on average, most survived only a couple of months post-splenectomy. Those treated with chemotherapy survived a bit longer. And early detection was the factor that had the greatest impact on longer survival rates. (4)

How to Prevent Spleen Cancer in Dogs

Unfortunately, canine spleen cancer can’t be prevented. The best thing that you can do as pet parents is try to catch it early, as removing malignant tumors before they have a chance to spread gives the best result.

Summary

Spleen cancer in dogs is relatively common. There are several types, depending on the cells involved. About 30 percent of dogs have the benign type, and 70 percent have malignant types, with most of those being hemangiosarcoma. 

Unfortunately, even with treatment, the prognosis for dogs with malignant spleen cancer is poor. Early detection (before the tumor spreads) is the best defense we have against this condition.

References

1. Spangler, W L, and P H Kass. “Pathologic factors affecting postsplenectomy survival in dogs.” Journal of veterinary internal medicine vol. 11,3 (1997): 166-71, doi: 10.1111/j.1939-1676.1997.tb00085.x.
2. Schick, Ashley R and Janet A Grimes. “Evaluation of the validity of the double two-thirds rule for diagnosing hemangiosarcoma in dogs with nontraumatic hemoperitoneum due to a ruptured splenic mass: a systematic review.” Journal of the American Veterinary Medical Association (2022): 1-5, doi:10.2460/javma.22.08.0389.
3. Corvera, Gloria, et al. “Pathological characterization and risk factors of splenic nodular lesions in dogs (canis lupus familiaris).” Animals, vol. 14, no. 5, 5 Mar. 2024, p. 802, doi: 10.3390/ani14050802. 
4. Wendelburg, Kristin M., et al. “Survival time of dogs with splenic hemangiosarcoma treated by splenectomy with or without adjuvant chemotherapy: 208 cases (2001–2012).” Journal of the American Veterinary Medical Association, vol. 247, no. 4, 15 Aug. 2015, pp. 393–403, doi: 10.2460/javma.247.4.393.