Soft Tissue Sarcomas in Cats

Soft tissue sarcomas are the result of uncontrolled cell growth in the soft tissues of the body. This can include muscles, nervous tissues, and connective tissues. They are notorious for being locally invasive but are not as likely to spread as other cancers. Soft tissue sarcomas are sometimes compared to an octopus, with the bulk of the tumor representing the head, and the microscopic invasive cells representing the tentacles.

Soft tissue sarcomas are common, especially in older cats, and are serious and can be life-threatening. Anytime there are lumps present, veterinary care is warranted. Regular veterinary visits may help to catch symptoms early and improve the outcome.

Soft tissue sarcomas arise from abnormal, uncontrolled growth of certain types of cells in the skin and subcutaneous connective tissues, including muscles, small blood vessels, and nerves. There is no single cause. Feline injection site sarcomas are associated with certain types of vaccines. Some soft tissue sarcomas are caused by a form of the feline leukemia virus called feline sarcoma virus. Any of these tumors can also be associated with radiation therapy, trauma, or foreign bodies (i.e., orthopedic implants).

Symptoms of soft tissue sarcomas are related to the tumor site and invasiveness of the tumor.

Diagnosis of a possible soft tissue sarcoma begins with a complete physical exam, blood work, and urinalysis. X-rays of the chest may be indicated to rule-out metastasis. CT, MRI, and ultrasound may also be utilized to fully characterize the tumor. Sampling of the tumor is essential for a definitive diagnosis, grading of the tumor, and guidance for treatment. Any enlarged lymph nodes may be biopsied as well.

If the tumor has not spread, surgical removal of the tumor is the treatment of choice. If the tumor has a clear outline, surgical excision can achieve a cure in 90% of patients. Often tumors recur if excision has been incomplete, and recurrent tumors tend to be more malignant. Injection site sarcomas in particular require very large surgical margins and have a high rate of recurrence (>90%). Radiation therapy may be initiated as an adjunct treatment in these cases. Chemotherapy in combination with surgery and/or radiation may also be useful if spread is present, and to reduce symptoms.

Prognosis depends on the grade of the tumor and the treatment chosen. The tumor grade is predictive of outcome and recurrence. In general, smaller, more superficial and slower-growing tumors are less malignant than larger, faster-growing tumors in deeper tissues. In cases of higher-grade, recurrent tumors, humane euthanasia may be considered.

As there is no single cause of soft tissue sarcomas, there is no clearly identified prevention. Soft tissue sarcomas are not contagious to humans, but feline sarcoma virus is contagious between cats. Appropriate vaccination and keeping cats indoors may prevent the feline sarcoma virus. The use of non-adjuvanted vaccines and avoidance of polyvalent vaccines can reduce the risk of injection site sarcomas. Vaccinations may be given in the limbs or tail to facilitate amputation if necessary.

Soft tissue sarcomas are common in cats. Fibrosarcomas are the most common type of soft tissue sarcoma in cats.

• Surgical excision
• Radiation
• Chemotherapy
• Symptomatic relief (palliation)
• Humane euthanasia