Soft Tissue Sarcomas in Cats and Dogs

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

How is the diagnosis made?
Soft tissue sarcomas can be challenging to distinguish from each other as well as from other types of tumors due to the
overlapping features and patterns. In human medicine, new tools became available (eg immunocytochemistry, tissue
microarrays) that have helped pathologists to better diagnose soft tissue sarcomas but their application in veterinary
medicine is still rather limited. Prior to initiating any type of treatment, it is important to gather as much information as
possible regarding the tumor's tissue origin, size, site, histologic grade (level of aggressiveness) and whether it has spread
to other organs.

Fine-needle aspirates are recommended to exclude other possible causes of suspected mass (eg abscesses, cysts, or
mast cell tumors), however,
cytologic evaluation by itself is usually not sufficient to reach a definitive diagnosis, and a
biopsy prior to initiating any type of treatment should be done. There are a variety of different biopsy techniques that can
be used but excisional biopsy is usually not recommended since surgery is typically performed after confirming diagnosis,
and multiple surgical attempts have a negative impact on survival for soft tissue sarcomas.

Additional tests are performed in order to evaluate how advanced the disease is. The tests will depend on the type of soft
tissue sarcoma but generally involve
blood and serum biochemical tests, chest X-rays and imaging. Blood tests are usually
normal for most pets but there are some exceptions. For example, blood abnormalities are commonly detected in dogs with
disseminated histiocytic sarcoma and hypoglycemia (low sugar) has been reported in dogs with intra-abdominal leiomyomas
and leiomyosarcomas (tumors of smooth muscle).

Imaging studies of the local tumor are usually done prior to planning the surgical removal of the tumor and/or radiation
therapy, especially in animals with suspected intra-abdominal soft tissue sarcomas. Advanced
imaging techniques such as
CT (computed tomography) and MRI (magnetic resonance imaging) are especially useful due to their high level of
resolution and detail. Other imaging methods can involve X-rays, ultrasound, angiography, and nuclear scintigraphy.

Evaluation of metastasis
Diagnostic tests that evaluate whether the tumors have spread to other organs include chest X-rays (to test for lung
metastasis), abdominal ultrasound (to check for metastasis in the spleen, liver) and fine-needle aspirates/biopsy of regional
lymph nodes (to check for lymph node metastasis). At the very minimum, chest X-rays should be performed prior to initiating
treatment since soft tissue sarcomas commonly spread to the lungs. Lymph node metastasis is not common for typical soft
tissue sarcoma but their biopsy/cytology should be assessed in animals whose lymph nodes appear abnormal and/or whose
specific tumor type is suspected to have a high metastatic potential.

Below are examples of soft tissue sarcomas seen in pets.

Does cancer cause pain in cats and dogs?
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 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?
Local tumor control is the most important consideration in the management of soft tissue sarcomas due to their locally
aggressive behavior. Surgical removal of the tumor is the main treatment of choice and radiation therapy is typically applied
in cases where the entire tumor could not be surgically removed. Specific treatment options will depend on the tumor
subtype, location, size, and how advanced the disease is. To learn more about treatment and/or prognosis for a specific
soft tissue sarcoma subtype, please click on the subtype of interest in the above table.

Soft tissue sarcomas aggressively invade adjacent tissues, necessitating the need for an aggressive surgery to prevent
local tumor recurrence (coming back). The first surgery provides the best opportunity for local tumor control. If the tumor
cannot be completely removed, radiation therapy is used to kill any remaining cancer cells, and provides an attractive
alternative to limb amputation for a limb affected with soft tissue sarcoma. Radiation therapy should be started a minimum of
7 days after the surgery to minimize the risk of radiation-induced complications within the surgical wound.

Radiation therapy
Radiation therapy can be used in combination with surgery to attempt cure or at least provide long-term control of the tumor
but it can also be used by itself for palliative reasons (provide pain relief associated with soft tissue sarcoma but not cure).
Current results indicate that radiation treatment is the best treatment option for tumors that could not be completely
surgically removed. Radiation therapy prior to surgery is becoming more common in veterinary oncology and is thought to
provide certain advantages: 1) the area subjected to radiation is smaller since after surgery, the entire surgical site must be
irradiated. 2) it shrinks the size of the tumor, making the following surgery easier. Human studies showed that there was no
difference in survival in patients who received radiation prior to surgery compared to those after surgery, however, wound
complications were significantly more frequent in pre-surgery radiation. Higher doses of radiation have a better chance of
killing the cancer cells but will also increase the chance of complications. Some studies suggest that combining radiation
hyperthermia can better control the local tumor but the difficulty of heating large tumors limits the utility of this approach

The benefit of chemotherapy in the treatment of soft tissue sarcomas is unknown, however, there are clinical situations in
which chemotherapy after surgery should be considered: dogs with grade III soft tissue sarcoma, metastatic disease, intra-
abdominal soft tissue sarcoma, and tumor types known to have a higher rate of metastasis. Drugs such as doxorubicin with
or without cyclophosphamide have shown most promise with 23% of dogs responding.

Finding a qualified veterinary oncologist
To locate a qualified veterinary oncologist in your area 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 soft tissue sarcoma in cats or dogs?
There are several clinical trials ongoing for dogs with soft tissue sarcomas, which are partially funded by the institutions. To
learn more about these trials, please visit the
Clinical Trials for Soft Tissue Sarcoma in Dogs 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?
The prognosis for soft tissue sarcoma is good. Local control of the tumor is very challenging and local tumor recurrence
rates after surgery (with or without radiation) range from 7% to 32%. Poor prognostic factors for local tumor recurrence
include large tumor size, incomplete surgical removal and high histologic tumor grade (high grade corresponds with
aggressive tumor behavior). Management of recurrent soft tissue sarcomas is usually more difficult than the original tumor,
emphasizing the need for an aggressive treatment of the initial tumor. Because the median time for tumor recurrence is 368
days, the pets should undergo long term follow up and frequent check ups. The metastatic rate for soft tissue sarcomas
varies from 8% to 17% with a median time to metastasis of 1 year, depending on the tumor's properties. The median
survival time for dogs with soft tissue sarcoma is 1416 days with surgical treatment and 2270 days with surgical and
radiation treatment. Overall, up to 33% of dogs eventually die of tumor related causes.

Additional online resources

  • 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  2/19/2017
Comprehensive guide to cancer diagnosis and treatment in cats and dogs

What are soft tissue sarcomas?
Soft tissue sarcomas is a general term that refers to a group of tumors that form in tissues of
mesenchymal origin such as the connective tissue (eg fat, smooth muscle, blood vessels, lymph
vessels, skeletal muscle, etc). They tend to have similar
histologic appearance and biological
behavior, and can be either benign (noncancerous) or malignant (cancerous). Soft tissue
sarcomas can arise in any part of the body although skin and subcutaneous (the layer of tissue
directly underlying the skin) tumors are the most commonly observed. The following table
classifies the known soft tissue sarcomas, their origin and potential for metastasis (spread to
other organs).

How common are these tumors?
These tissues represent 15% of all skin tumors and 7% of all subcutaneous tumors in cats and
dogs. Most soft tissue sarcomas are solitary tumors in middle to older aged pets and tend to be
over-represented in large breed dogs.
Tissue of
Malignant tumor
Primary sites
Risk of
Organ of
Adipose (fat)
Limbs, abdominal or chest cavity
Low to moderate
Lungs, liver, spleen,
Fibrous tissue
Limbs, oral cavity
Low to moderate
Histiocytic cells
Histiocytic sarcoma
Moderate to high
Lymph nodes, lungs,
spleen, liver, kidneys
Lymph vessels
Lymph nodes
Blood vessels
Spleen, heart, liver, muscle, bone,
Lungs, liver, lymph
nodes, distant
dermal sites
Nervous tissue
Peripheral nerve
sheath tumor
Low to moderate
Tongue, larynx, heart, bladder
Low to moderate
Lungs, liver, spleen,
Smooth muscle
Gastrointestinal,spleen, liver, vulva,
vagina, subcutaneous tissue
Lymph nodes, liver,
spleen, kidneys
Synovial tissue
Synovial cell
Moderate to high
Lymph nodes, lungs
Myxoma tissue
Limbs, joints
Low to moderate