Spleen Tumors in Cats and Dogs
Comprehensive guide to cancer diagnosis and treatment in cats and dogs
What are spleen tumors?
Spleen is an organ that performs a variety of functions that include storing blood, removal of old or damaged red blood
cells (essentially functioning as a filter), and helping the immune system. Although it performs these functions, one can live
without a spleen if necessary. Dogs and cats can develop tumors in the spleen, which can be either benign (non-
malignant) or malignant. In dogs, most malignant spleen tumors are malignant hemangiosarcomas (45-51% of all spleen
tumors); in cats, most frequent spleen tumors are mast cell tumors or lymphosarcomas.

Spleen hemangiosarcoma (also known as hemangioendothelioma or angiosarcoma) is a malignant cancer that arises out
of blood vessels. It may be present as a single tumor or as multiple tumors, and often ruptures and bleeds. It occurs more
frequently in dogs compared to other species (accounts for ~7% of all canine cancers) and is mostly seen in middle-aged
to older animals. German Shepherds, golden retrievers, and Labrador retrievers appear to be at higher risk.

What are the symptoms of spleen tumors in cats and dogs?
The symptoms can include nonspecific signs (e.g. chronic weakness, lack of appetite, weight loss), abdominal swelling,
collapse and acute death if the tumor ruptures and bleeds internally.

How is the diagnosis of spleen tumors made in cats and dogs?
The tests used to diagnose spleen cancer include physical examination (where the tumor can be felt by the examining
veterinarian), blood tests (spleen tumors are often associated with deficiency of red blood cells), ultrasound and other
imaging studies if necessary.

Does cancer cause pain in pets?
Pain is common in pets with cancer, with some tumors causing more pain than others. In addition to pain caused by the
actual tumors, pets will also experience pain associated with cancer treatments such as surgery, radiation therapy or
chemotherapy. Untreated pain decreases the pet's quality of life, and prolongs recovery from the illness, treatment or
injury. It is, therefore, essential that veterinary teams that are taking care of pets with cancer should also play a vital role in
educating pet owners about recognizing and managing pain in their pets. The best way to manage cancer pain in pets is to
prevent it, a term referred to as preemptive pain management. This strategy anticipates pain ahead of time and
administers pain medication before the pet actually experiences pain, thus ensuring the pet's maximum comfort.

To learn more about which tumors are likely to cause a lot of pain, how to recognize pain in pets with cancer and what
cancer pain management options are available for your pet, please visit the
Cancer Pain Management section.

Is nutritional support important for pets with cancer?
Cancer cachexia (a term referring to progressive severe weight loss) is frequently observed in pets with cancer. Pets with
cancer lose weight partly because of lack of appetite and partly because of cancer-induced altered metabolism. Some of
the causes for decreased appetite are related to the cancer itself (for example, tumors may physically interfere with food
chewing, swallowing, and digestion process) and some may be related to the side effects of cancer treatment (for example,
some chemotherapy drugs cause nausea and vomiting, and radiation therapy can cause mouth inflammation).

Proper nutrition while undergoing cancer treatment is essential to maintain your pet's strength, improve survival times,
quality of life and maximize response to therapy. Adequate nutritional support was shown to decrease the duration of
hospitalization, reduce post-surgery complications and enhance the healing process. Additionally, pets with cancer need to
be fed diets specifically designed to provide maximum benefit and nutritional support for the patient. To learn more, please
visit the
Cancer Nutrition section.

What are the treatment options for spleen cancer in cats and dogs?
Surgical removal of the spleen (called splenectomy) has been the treatment of choice for spleen tumors. Dogs undergoing
spleen surgery are at risk of developing heart arrhythmias - one study of 59 dogs showed that 24% develop arrhythmias
but they usually resolve 24 to 48 hours. Most dogs will go home 1-2 days after surgery. The most common complication
during surgery is bleeding. Spleen may begin to bleed at any time, which may necessitate blood transfusion. Some pets
receive blood transfusion even prior to the surgery just to make sure that the pet has enough red blood cells in case the
spleen begins to bleed during surgery. Because it may not be known for sure whether the spleen mass is actually benign
(non-cancerous) or malignant prior to the surgery, you should discuss with your veterinary surgeon what your wishes are
once (s)he opens up the belly and can have a clearer picture of what kind of tumor is actually present . For example, if the
spleen tumor is malignant and already extensively spread in the abdomen, do you still want to proceed with surgical
removal of the spleen and try chemotherapy afterwards? Or would you rather have the pet awaken without undergoing the
surgery, or have the pet euthanized while anesthesized? All of these questions should be discussed before the decision to
operate is made.

Chemotherapy drugs (doxorubicin with or without vincristine/cyclophosphamide) have recently become important for
treatment of spleen hemangiosarcomas given the tumor's high metastatic potential. In cases where surgery cannot be
performed, doxorubicin-based chemotherapy is applied to achieve temporary tumor shrinkage. For dogs with existing
cardiac (heart) disease, another drug called epirubicin may be an alternative. In a retrospective study with 59 dogs with
spleen hemangiosarcoma,  dogs treated with surgery and epirubicin lived longer (144 days) compared to dogs treated with
surgery alone (86 days). Of18 dogs treated with epirubicin, seven were hospitalized due to gastrointestinal toxicities (
et al
, J Am Vet Med Assoc, 2007).

Radiation therapy is rarely used for spleen hemangiosarcoma due to the organ's location.

Immunotherapy in combination with chemotherapy may be an additional option for dogs whose spleen hemangiosarcoma is
surgically removed.  In a study with 32 dogs with Stage I/II spleen hemangiosarcoma (tumors that have not yet spread to
distant organs), all dogs received chemotherapy (doxorubicin and cyclophoshamide) after surgery but half the dogs also
received L-MTP-PE (a synthetic derivative of bacterial cell wall component) whereas the other half received placebo (an
inactive treatment to serve as a control). In this study, ~37% of dogs who received L-MTP-PE were disease-free after one
year compared to only 15% of dogs who did not receive L-MTP-PE. Dogs with Stage I disease had median disease-free
survival of 212 days (length of time after treatment during which half the pets had no sign of disease) and median overall
survival of 355 days (time from treatment at which half of the pets are still alive) compared to dogs with Stage II disease
(122 days for median disease-free survival and 148 days for median overall survival) (
Vail et al, Clinical Cancer Research,

How do I find a qualified veterinary oncologist?
To locate a qualified veterinary oncologist worldwide who can discuss with you appropriate cancer treatment plan for your
pet's cancer condition, please visit the "
Locate a veterinary oncologist" section.  

Are there any clinical trials investigating new treatments for spleen cancer in cats and dogs?
There are several available clinical trials (partially or fully funded by the institutions) investigating new treatments for
spleen hemangiosarcomas in dogs. To learn more about these clinical trials, please visit
Clinical Trials for Spleen
Hemangiosarcoma section.

Additionally, there are several clinical trials available for cats and dogs with any tumor type for which your pet may qualify.
To learn more these trials (which are partially or fully funded by the institutions), please visit the
Dog Clinical Trials (any
tumor type) or Cat Clinical Trials (any tumor type) section.  

To learn more about veterinary clinical trials in general, please visit the
Pet Clinical Trials section.

What is the prognosis for spleen tumors in cats and dogs?
If the spleen tumor is benign and the pet survived surgical removal of the spleen, the prognosis is good. If the spleen tumor
is hemangiosarcoma (HSA), the prognosis will depend on the cancer stage (higher number indicates more extensive
disease; Stage IV refers to a tumor that spread to distant organs in the body).

The prognosis for pets with spleen HSA is poor despite aggressive
surgery and chemotherapy. Spleen hemangiosarcomas
are very aggressive tumors with a rapid onset of
metastasis (spread) to other organs. The most frequent organs to which
hemangiosarcomas metastasize are the liver and lungs, but they have also been reported to spread to the kidneys,
muscle, lymph nodes, adrenal glands, and brain.The earlier the spleen HSA is detected, the better the prognosis. For
example, in one retrospective study of 59 dogs with spleen HSA, dogs with Stage I disease had median survival time of 345
days compared to 93 days for Stage II spleen cancer and 68 days for Stage III spleen cancer (
Kim, J Am Vet Med Assoc,

Median survival times for dogs with spleen HSA treated with
surgery alone range from 19 days to 3 months, and less than
10% of animals are alive after one-year when treated with surgery. Doxorubicin-based
chemotherapy after spleen surgery
has been reported to increase the median survival time to 141 to 179 days but less than 10% of animals still remain alive
one year post-sugery. One study showed that adding
immunotherapy (L-MTP-PE) increased survival to a median of 273
days. Some studies suggest that animals with non-ruptured spleen tumors have a more favorable prognosis when
chemotherapy is used compared to those whose tumors are ruptured.

Source: Withrow Stephen J, and David M. Vail. Small Animal Clinical Oncology. St Louis: Saunders Elsevier, 2007.

Additional online resources about spleen cancer in pets:

  • Withrow Stephen J, and David M. Vail. Small Animal Clinical Oncology. St Louis: Saunders Elsevier, 2007.
  • Morrison Wallace B. Cancer in Dogs and Cats: Medical and Surgical Management. Baltimore: Williams&Wilkins, 1998
© 2007 Pet Cancer Center. ALL RIGHTS RESERVED.
Last updated 2/20/2017
Study treatment
Number of dogs
Median Survival Time (Days)
Surgery alone
  19-86 days
Surgery + mixed bacterial vaccine
Surgery + mixed bacterial vaccine +
Surgery + Ifosfamide
Surgery + vincristine/doxorubicin/cyclophosphamide
Surgery + doxorubicin/cyclophosphamide
Surgery + doxorubicin/cyclophosphamide
Surgery + doxorubicin/cyclophophosphamide + L-MTP-PE
  • Hemangiosarcoma is the most common spleen tumor in dogs
  • Common symptoms include weakness, abdominal swelling, collapse or acute death if the tumor ruptures
  • Spleen hemangiosarcomas are very aggressive with a rapid onset of metastasis to other organs
  • Surgical removal of the spleen with or without chemotherapy is the current standard of care
  • Prognosis for spleen hemangiosarcoma is poor with <10% of dogs alive one year post-treatment
  • The earlier the spleen hemangiosarcoma is detected, the better the prognosis.