Soft Tissue Sarcomas

What is a soft tissue sarcoma?

Soft tissue sarcomas are a broad category of tumors that develop from connective tissue, muscle, or nervous tissue in dogs and cats. They form when these cells begin growing and dividing uncontrollably.

Because connective, muscle, and nervous tissues are found throughout the body, these tumors can develop almost anywhere, including the chest, back, side, legs, and face.

Soft tissue sarcomas account for about 8% to 15% of skin cancers in dogs and about 7% to 9% of skin cancers in cats. Fibrosarcomas are common in dogs and are a type of soft tissue sarcoma. Although soft tissue sarcomas arise from different types of cells, they tend to behave similarly and are often treated in the same way.

What are the signs of soft tissue sarcomas?

The signs depend on the tumor’s location and the tissues it affects. Often, pets have a noticeable lump or mass that continues to grow. Signs associated with soft tissue sarcomas may include:

• A firm and growing lump or mass
• Pain in the affected area
• Swelling of a limb
• Limping or difficulty walking
• Weakness or loss of function in a limb
• Vomiting, diarrhea, lack of appetite, weight loss, or abdominal pain (for intestinal tumors)
• Bad breath, difficulty eating, loss of appetite, bleeding from the mouth, or obvious tumors in the mouth (for oral tumors)
• Difficulty with urinating or defecating (for some tumors affecting the reproductive system)

What causes soft tissue sarcomas?

The reason why a particular pet may develop this, or any tumor or cancer, is not straightforward. Few tumors and cancers have a single known cause. Most develop because of a complex combination of environmental and genetic factors. For most soft tissue sarcomas, no specific cause can be identified. Sarcomas at injection sites occur in cats but are rare in dogs. Cats exposed to feline sarcoma virus (a form of feline leukemia virus) may develop sarcomas on the head and neck.

How are soft tissue sarcomas diagnosed?

During a fine needle aspiration (FNA), a small needle is used to collect cells from a lump or mass. The cells are then placed on a microscope slide and examined to help diagnose the condition.In some cases, a fine needle aspiration (FNA) may be performed. FNA involves using a small needle and syringe to collect a sample of cells from the tumor. The cells are placed on a microscope slide, and a veterinary pathologist examines them under a microscope.

If FNA does not provide a diagnosis, your veterinarian may recommend a biopsy. A biopsy is the surgical removal of a piece of the tumor. A veterinary pathologist then examines the tissue under the microscope. This process is called histopathology. A biopsy helps determine how aggressive the tumor is and guides treatment decisions.

Your veterinarian may recommend staging, which involves checking whether the cancer has spread to other parts of the body. This may include bloodwork, urinalysis, radiographs (X-rays) of the lungs, and possibly an abdominal ultrasound. If enlarged or abnormal lymph nodes are present, your veterinarian may collect additional samples to determine whether the cancer has spread.

How do these tumors typically progress?

How these tumors behave depends on their location and grade. In general, higher-grade tumors (graded I to III) are more likely to spread to other parts of the body. However, soft tissue sarcomas often invade nearby tissues. These tumors can be compared to an octopus: the visible tumor forms the body, while microscopic extensions spread into surrounding tissue like tentacles. These hidden extensions can make radiation or complete removal difficult.

What are the treatments for these types of tumors?

Treatment may include surgery, radiation therapy, chemotherapy, or a combination of these approaches.

Surgery

The most common treatment for soft tissue sarcomas is surgery. Because these tumors often extend microscopic "tentacles" into nearby tissue, surgeons must remove a wide margin of normal tissue around the tumor to reduce the risk of recurrence. If histopathology shows that tumor cells remain after surgery, your veterinarian may recommend a second surgery, radiation therapy, or a combination of both treatments.

Radiation Therapy

Radiation therapy is often used when complete surgical removal is difficult or when tumor cells remain after surgery. Radiation can help control tumor regrowth and reduce the chance that the tumor will return in the same area.

Chemotherapy

Chemotherapy is not usually the first treatment choice. Your veterinarian may recommend chemotherapy when surgery or radiation therapy is not possible because of the tumor's size or location. Chemotherapy may also be used after surgery in some cases. 

• Metronomic chemotherapy: Low-dose chemotherapy given more frequently than traditional chemotherapy. 
• Localized chemotherapy: Chemotherapy delivered directly to the tumor site, such as the placement of cisplatin beads or gel.

Your veterinarian will discuss these options with you if they are appropriate for your pet's particular type of sarcoma.