Joint Cancer (Synovial Sarcoma) in Cats

Synovial Sarcoma in Cats

The synovial membrane is the layer of soft tissue that lines the surfaces within the joints, such as those between the joints at the knees and elbows. Synovial sarcomas are soft tissue sarcomas – malignant cancers – that arise from the precursor cells outside the synovial membrane of the joints and bursa (the fluid-filled, sac-like cavity between joints that helps to facilitate movement).

Precursor cells have the ability to differentiate into one or two closely related  forms: epithelial cells (skin cells) or fibroblastic (connective tissue) cells. Consequently, the tumor may have cancer resembling both cancers of the skin and of the connective tissue.

Synovial sarcomas are aggressive and highly locally invasive, spreading in greater than 40 percent of cases. They most often spread to the elbow, knee, and shoulder blade regions. This type of cancer is rare in cats.

Symptoms and Types

• Limping
• Slowly progressive lameness
• Palpable mass
• Weight loss
• No appetite (anorexia)    

Causes

• Unknown

Diagnosis

You will need to provide a thorough history of your cat's health and onset of symptoms. Your veterinarian will then perform a complete physical exam and order standard laboratory tests, including a biochemical profile, a complete blood count, a urinalysis and an electrolyte panel to rule out other non-cancerous causes for your cat's symptoms. 

Visual diagnostic techniques will show abnormalities around the affected joints. X-rays of the mass will show that the tumor is involved in both the bone and the joint. To obtain a definitive diagnosis, a biopsy of the soft and bony tissue of the tumor is necessary for histologic evaluation (microscopic analysis of the tissue sample). Using fine-needle aspirates (removal of fluid), the regional lymph nodes (i.e., the lymph nodes of the groin, armpits) should also be sampled and tested for evidence of metastasis (spread). 

Treatment

The invasiveness of this type of sarcoma makes amputation (if possible) of the affected limb the treatment of choice. When appropriate, the patient should be treated with supportive chemotherapy. Pain medication will also be prescribed and administered as necessary.

Living and Management

After surgery, you should expect your cat to feel sore. Your veterinarian will give you pain medication for your cat to help minimize discomfort, and you will need to set up a place in the house where your cat can rest comfortably and quietly, away from other pets, active children, and busy entryways. Setting the cat litter box and food dishes close by will enable your cat to continue to care for itself normally, without exerting itself unduly. Use pain medications with caution and follow all directions carefully; one of the most preventable accidents with pets is overdose of medication.

Your veterinarian will schedule follow-up appointments with you for your cat every two to three months for the first year after diagnosis of the synovial sarcoma. After the first year your cat may be seen by your veterinarian every six months for follow-up exams, and to affirm that the cancer has not recurred. X-rays should be taken at each visit to check for local recurrence and to confirm that the cancer has not spread to the lungs.