Splenic Mass in Dogs: What You Need to Know

The dog’s spleen is a highly vascular organ that sits behind the stomach. The spleen’s function is a red blood cell processing plant. It filters red blood cells, getting rid of old, damaged, or infected cells. It also stores healthy red blood cells, ready to contract and release these into circulation in the case of emergent need. The spleen is a very helpful organ! Unfortunately, in dogs, the spleen is also a common site for the development of tumors or masses. 

Not all tumors or masses are cancerous (malignant); some are benign (noncancerous). The prognosis for a dog with a malignant splenic mass is not good, but surgery to remove a benign mass is curative. 

Unfortunately, it’s exceedingly difficult to tell if a splenic mass is benign or malignant until the spleen is removed and submitted for biopsy. If your veterinarian detects a mass in your dog’s spleen, it’s likely that you will have to decide whether to go ahead with surgery to remove the spleen before you know whether the surgery can prolong your dog’s life.

What Are the Expected Outcomes of a Splenic Mass in Dogs?

The most fortuitous scenario involving a splenic mass occurs when the tumor is discovered by palpation on a routine veterinary physical examination. Benign tumors tend to grow to large sizes without otherwise causing problems, increasing the likelihood they’ll be picked up on physical exam. (This should underline the importance of annual or, even better, twice-annual physical exams for middle-aged and senior dogs.)

Discovering a splenic mass in this way, before it ruptures, gives you the opportunity to have an abdominal ultrasound performed. Ultrasound can confirm the mass is in the spleen and can be used to look for any evidence of metastasis (cancer spread) in the abdomen.

Chest x-rays may also be recommended to make sure there is no metastasis to the lungs. If the chest x-ray and abdominal ultrasound show no obvious cancer spread, surgery to remove the spleen should be considered.

Life Expectancy of a Dog With a Splenic Mass

If the splenic mass proves to be benign, the surgery will have extended your dog’s life. While benign masses won’t spread to other organs, they can still rupture and cause your dog to bleed internally, so their removal is necessary for your dog’s survival. A study published in 2018 in the Journal of Veterinary Science found that the two-year survival rate for of dogs who underwent a splenectomy for a benign mass was nearly 78%.

Another study published in 2016 in the Journal of the Veterinary Medical Association found that the median life expectancy of dogs with benign splenic masses was 436 days and that dogs with malignant splenic masses was just 110 days.

If those numbers don’t make it clear, I’ll clarify: Yes, your dog can live without a spleen. She may be more prone to certain infections and less effective at rapidly replacing red blood cells in a crisis, but for the most part, her other organs will step up and take over for the missing spleen.

Spleen Cancer in Dogs: Malignant Splenic Masses

Let’s go back a step. Say your veterinarian has detected a splenic mass in the course of a physical exam, follows up with an ultrasound, and finds that the mass has metastasized. 

Malignant splenic masses frequently metastasize to the liver or heart. Either one is bad news, but you may find comfort in the certainty of the knowledge that your dog’s prognosis is poor. Most dogs with malignant splenic masses succumb to their disease within a few months, sometimes even weeks, of surgery. Chemotherapy, used alone or in conjunction with surgery to remove the splenic mass, may slightly improve a dog’s prognosis, depending on the type of malignancy. 

There are tools (biopsy, fine-needle aspirate) that, theoretically, could be used in an attempt to determine whether a splenic mass that has not metastasized is malignant, but they are typically inconclusive and the risk of hemorrhage during and after the procedure is high. 

The Worst-Case Scenario: Splenic Mass Rupture in Dogs

Unfortunately, many splenic masses are not detected in the course of a routine exam, but are discovered while diagnosing a dog in the midst of an out-of-the-blue medical crisis. 

Here is an all-too-common scenario: Your happy and seemingly healthy 10-year-old Golden Retriever is out in the yard chasing balls with the kids, when she suddenly collapses. She looks confused, and though she is alert and responds to you, she is too weak to get up, and she is breathing faster than usual. 

You rush her to the emergency veterinary hospital, where the attending vet has a pretty good idea what’s going on as soon as she looks at her gums, which are ghostly white, and feels her abdomen, which has fluid in it. Bloodwork (showing decreased circulating red blood cells) and abdominal x-rays confirm the original clinical suspicion: Your dog has a splenic mass that has ruptured. She is bleeding internally, and without immediate surgery and blood transfusions, she is going to die.

In this scenario, there isn’t time to wait for the results of any tests that may determine whether the mass is malignant (with a poor prognosis) or benign (in which case, surgery may save your dog’s life); you will have to decide on the spot whether to give your veterinarian the go-ahead for emergency surgery to try to stop the bleeding and to remove the dog’s spleen, or to euthanize your dog. It’s a wrenching decision. 

No Sure Test for Spleen Cancer in Dogs

Knowing if a tumor is malignant or benign before surgery would help a lot, given the grave prognosis associated with malignant tumors of the spleen. Unfortunately, at this time, there is no definitive way to answer that question preoperatively, although we may be getting closer (see “A Potentially Helpful Tool,” above). This leaves you facing a difficult decision for your dog, and makes one wonder – and fear – how many dogs with benign tumors are euthanized, when they might have been cured.

There are some generalizations that may help you make the decision to give your veterinarian the go-ahead for surgery or to euthanize your dog in order to prevent a traumatic death:

• Large, non-ruptured splenic masses found on routine physical exam have the best chance of being benign.
• Small-breed dogs with splenic masses have a better prognosis in general than the larger breeds.
• About two-thirds of all splenic masses in dogs are malignant.
• If you have an older large-breed dog with a splenic mass that has ruptured, the likelihood of this being a benign situation is very low.
• Heritability contributes to the risk of malignant splenic masses; hemangiosarcoma is common in certain breeds, including Golden Retrievers, German Shepherds, and Portuguese Water Dogs. If a dog who is closely related to your dog has had a malignant mass, the chances are higher that your dog will, too.