Soft Tissue Sarcomas

What is a soft tissue sarcoma?

Soft tissue sarcomas are a broad category of tumors including those that arise from the connective, muscle, or nervous tissues in dogs and cats. These tumors are the result of abnormal production of these cell types in an uncontrolled manner. Connective, muscle, and nervous tissues are present throughout the entire body; therefore, these tumors can develop over the chest, back, side, legs, and facial tissues of your pet.

Soft tissue sarcomas make up about 15% of cancers of the skin affecting dogs and about 7% of those affecting cats. Fibrosarcomas are common in dogs and are a type of soft tissue sarcoma (see handout "Fibrosarcoma in Dogs" for more information).

"Soft tissue sarcomas make up about 15% of cancers of the skin affecting dogs and about 7% of those affecting cats."

Even though soft tissue tumors arise from many different types of cells, they all behave in a similar manner and their treatment is typically the same.

What causes soft tissue sarcomas?

The reason why a particular pet may develop this, or any tumor or cancer, is not straightforward. Very few tumors and cancers have a single known cause. Most seem to be caused by a complex mix of risk factors, some environmental and some genetic or hereditary.

For most cases of soft tissue sarcomas, no direct cause has been determined for their development. Sarcomas at injection sites occur in cats but are rare in dogs (see handout “Post-Vaccination Sarcoma in Cats” for further information on this type of sarcoma). In cats exposed to a form of the feline leukemia virus (called feline sarcoma virus), the development of sarcomas on the head and neck sometimes occurs.

What are the clinical signs of soft tissue sarcomas?

The clinical signs depend on where the tumor is located and the tissues that are affected. Often, pets have a noticeable mass that is growing in size.

Signs associated with soft tissue sarcomas include the following:

• Pets that have tumors arising from muscle tissue may show signs of pain in the affected region and may have a distinct firm and growing mass (tumor).
• Tumors that are located on the limbs may cause changes in your pet’s ability to walk and the limbs may have obvious swelling.
• Pets that have tumors arising from nervous tissue may be unable to use the affected limb or may show other neurological signs.
• Pets with intestinal tumors may have signs of an intestinal blockage, such as vomiting, diarrhea, lack of appetite, weight loss, and abdominal pain.
• Pets with soft tissue sarcomas in the mouth often have halitosis (bad breath), difficulty eating, loss of appetite, bleeding in the mouth, or obvious tumors in the mouth.
• Signs of a soft tissue sarcoma affecting the reproductive system depend on the location of the tumor. For example, if the prostate is affected, difficulty with urinating or defecating may be observed.

How are soft tissue sarcomas diagnosed?

In some cases, a fine needle aspiration (FNA) may be performed. FNA involves taking a small needle with a syringe to suction a sample of cells directly from the tumor and placing them on a microscope slide. A veterinary pathologist then examines the slide under a microscope. If a diagnosis is not confirmed by this method, a biopsy may be needed. A biopsy is a surgical excision of a piece of the tumor. Pieces of the tumor are then examined under the microscope. This is called histopathology. A biopsy is beneficial because it gives an indication as to how aggressive the tumor is and how its treatment should be approached.

Staging (searching for potential spread to other locations in the body) may be recommended. This may include blood work, urinalysis, radiographs (X-rays) of the lungs, and possibly an abdominal ultrasound. If any lymph nodes are enlarged or feel abnormal, further sampling may be pursued to determine if any spread is present.

"If any lymph nodes are enlarged or feel abnormal, further sampling may be pursued to determine if any spread is present."

How do these tumors typically progress?

This is entirely dependent on the location and grade of the tumor. Typically, the higher the grade (these tumors are graded from I to III) the more likely that spread is possible. However, one of the biggest concerns with soft tissue sarcomas is their ability to invade the local surrounding tissues. They can almost be described as an ’octopus’, where the bulk of the tumor is the head and the microscopic cells that invade the surrounding tissue are like small tentacles. These ‘tentacles’ become challenging to treat when managing your pet’s tumor, either by surgery or radiation therapy.

"...one of the biggest concerns with soft tissue sarcomas is their ability to invade the local surrounding tissues."

What are the treatments for these types of tumors?

The most commonly pursued treatment for all soft tissue sarcomas is surgery. Because these tumors typically produce ‘tentacles’ of abnormal cells, wide margins (the amount of tissue that needs to be removed) must be obtained for the best control of the tumor. If microscopic cells are left behind after surgery, recurrence of the tumor is much more likely. If cells are left behind (determined through histopathology), either a second surgery or a combination of surgery and radiation therapy may be pursued.

Chemotherapy is not usually pursued as a primary treatment unless surgery or radiation are not options for your pet based on the tumor size or location. Chemotherapy may be an option after surgery. Metronomic chemotherapy (daily administration of lower doses of chemotherapy rather than traditional schedules) may be recommended. These therapies will be discussed with you if they are relevant to your pet’s particular type of sarcoma.