Soft Tissue Sarcomas In Cats

Feline soft tissue sarcomas are malignant tumors that can occur anywhere on the outside of a cat’s body. They arise out of the skin and subcutaneous connective tissues, including muscles, small blood vessels, fat and nerves. For the most part, soft tissue sarcomas tend to be slow growing. However, there are some instances where this type of tumor can be aggressive and spread quickly. Approximately 7% of all skin cancers in cats will be soft tissue sarcomas¹.

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The most common symptom of soft tissue sarcomas in cats is a lump or a mass. Some cats will also limp or adjust their gait if the tumor is on a limb or in an area that would impede their movement.

Types Of Soft Tissue Sarcoma

Although soft tissue sarcomas are more common in dogs, they do occur in cats. These tumors often appear to be encapsulated, but they have tendrils or finger-like projections that can be invasive to the surrounding normal tissue. These tendrils can make it difficult to cleanly remove the entire growth through surgery. If any of the tendrils are left, there is a possibility that the soft tissue sarcoma will recur.

The following are just four types of sarcomas in cats:

• Fibrosarcoma: This is a cancerous growth presenting as a mass on the body or leg of a cat.
  
• Injection-site sarcoma: A tumor that develops at the site of a vaccine injection, such as for rabies or feline leukemia. While the treatment is the same as other sarcomas, these tend to be more a more aggressive form of the disease.
• Liposarcoma: Liposarcomas are rare tumors that originate in a cat’s fat tissue.
• Nerve Sheath Tumors: These tumors arise from the covering or the sheath of a nerve.  They present as masses or lumps on a limb or the body.  In a rare case, they can  be painful and may even result in paralysis of the affected limb. If the tumor can be removed, the cat’s leg mayreturn to normal.

Soft tissue sarcomas are more likely to occur in older cats. Other factors — such as a cat’s sex or breed — do not seem to make a difference as to whether a feline will develop a soft tissue sarcoma.

Clinical Signs Of Sarcoma In Cats 

The clinical signs of a feline soft tissue sarcoma can vary depending on its location and the tissue that is being affected. The following are some of the symptoms or signs you may notice if your cat develops this type of tumor:

• A lump or mass: These are typically slow growing
• Lameness: If the mass is located on one of your cat’s limbs or in an area that could restrict your feline’s movements, your cat may limp
• Pain: Soft tissue sarcomas are typically painless, but some — such as ones that develop in the myelin sheath — can cause pain. Thankfully, this is rare. 

Diagnostics & Staging 

If your cat has a mass, your vet will want to determine if it could be benign — such as a lipoma or a cyst — or if it is a soft tissue sarcoma or another form of cancer. The following are some of the diagnostic tests that might be performed on your cat:

• Blood Analysis: This test is to check on your cat’s general health and organ function.
• Fine Needle Aspiration: A needle will be inserted into the mass and cells will be removed and examined under a microscope. Because these types of tumors do not release cells from the mass easily, your veterinarian may need to perform other tests to ensure that the growth is not a soft tissue sarcoma.
• Tissue Biopsy: Vets use this test to make a definitive diagnosis and to determine its aggressiveness.
• Three-view Chest X-rays and/or Abdominal Ultrasounds: These tests will show if the cancer has spread to other areas in the body.

Depending on the type of soft tissue sarcoma, your veterinarian may also have to perform other tests.

Treatment Options

If the cancer has not spread, your veterinary oncologist may suggest the following treatment options:

Surgery

Surgical treatment requires wide margins around the tumor in order to be successful. If there is room for that wide margin or if the affected limb needs to be amputated, surgical treatment can be curative in approximately 90% of cases.

If the margins are not clean, however, there is a chance that the soft tissue sarcoma could recur within six to eight months.

Radiation Therapy

Your veterinary oncologist may also suggest radiation treatment, which could put the cancer into remission for a relatively long period of time. There is also a more advanced form of radiation therapy called stereotactic radiation (SRS/SRT). This treatment allows your veterinary oncologist to deliver high doses of radiation precisely and directly to the growth or mass. In most cases, this results in more damage to the tumor while sparing the surrounding tissues. In addition, SRS/SRT treatments typically have fewer and less severe side effects than conventional radiation therapy.

Update: Stereotactic radiation (SRS/SRT) can now be delivered safely and effectively to cancer patients who have undergone surgery to remove a tumor but are still found to have residual cancer. This advancement was tested through a PetCure clinical trial conducted between May 2017 and March 2019 with findings published in the July 2023 edition of JAVMA, providing new hope for many dogs and cats that are in need of additional cancer care after undergoing tumor-removal surgery. This cutting-edge technology allows for the insertion of a liquid fiducial marker at the tumor site, either during or after surgery, providing a necessary target for radiation therapy treatment planning.  This innovative approach offers new hope for our furry companions in their fight against cancers like soft tissue sarcoma, mast cell tumors and adenocarcinoma like those found in anal sac adenocarcinoma.

Chemotherapy

Given by intravenour form or oral pills, chemotherapy is sometimes used to treat more aggressive tumors. Pairing chemotherapy with radiation therapy could help slow down the recurrence of soft tissue sarcomas.

If the Sarcoma Has Spread

If your veterinary oncologist determines that the sarcoma has spread, he or she may suggest using a combination of chemotherapy, surgery and radiation therapy to slow the growth. Although this treatment will likely not cure the cancer, it could slow its progression.

Without treatment, your cat’s soft tissue sarcoma will continue to grow, usually slowly. In time, however, it may grow large enough to impact your feline’s day-to-day life.

Prognoses & Life Expectancy

When it comes to soft tissue sarcomas in cats, life expectancy depends on the grade of the tumor and the type of treatment chosen. If the tumor is not completely removed during surgery or with radiation treatment, it is likely to recur within a year³. The good news is that if the tumor is completely eliminated, approximately 90% of felines will live without the soft tissue sarcoma recurring.

Even cats with high-grade tumors can benefit from treatment. For example, treating a cat with a combination of surgery, chemotherapy and radiation can give the feline a 50% chance of surviving for another two years³.

For More Information

If your cat has recently been diagnosed with a soft tissue sarcoma, find your local PetCure Oncology. Our caring and understanding staff can give you more information about our treatments and services.