Joint Tumors (Synovial Cell Tumors)

Synovial cell sarcomas originate from the synovium, or the lining of joints. Normally there are three types of cells that form the synovium: phagocytic macrophages (a cleaning cell that eats debris); antigen-presenting dendritic cells (help the body to recognize foreign material and bacteria in the joint); and fibroblast-like mesenchymal cells that produce glyosaminoglycans (joint lubricant).

Common features
Synovial cell tumors have a common set of features. They 1) can develop in any joint in the body, 2) have poorly defined microscopic margins, 3) have roots that infiltrate through tissue planes around the joint, 4) commonly regrow after conservative surgery, 5) spread through the blood stream and 6) respond poorly to radiation and chemotherapy when used without the addition of surgery.

Swelling surrounding a joint is the most common finding of a synovial cell sarcoma. Most sarcomas have a firm consistency; however, some have a softer texture. Once these tumors get larger, they may become ulcerated and develop a secondary infection. As the tumor grows, it commonly will cause the pet to become lame on the affected limb. If the tumor has spread to the lungs, breathing difficulty may be seen. Spread of the tumor to other organs may cause loss of appetite, weight loss and general discomfort.

Diagnosis of synovial cell sarcoma is based on a biopsy performed by aspirating the tumor with a small needle or surgically collecting a piece of tissue from the mass. These tumors may not exfoliate cells very well as the cells may be tightly fixed together, thus necessitating a surgical biopsy. An X-ray of the tumor commonly shows soft tissue swelling around the joint and in some cases erosion of the bones. A complete blood count, chemistry profile and urine testing are done to evaluate the health status of your companion’s internal organs prior to anesthesia and surgery. Chest X-rays are used to help rule out spread of cancer to the lungs and lymph nodes in the chest. Abdominal ultrasound is also performed to rule out spread of tumor to the internal abdominal organs.

For the best outcome, amputation of the limb is the treatment of choice for synovial cell sarcomas.

Chemotherapy may be indicated to help stunt the growth of metastatic cancer from a high-grade sarcoma. In the literature, there is not overwhelming evidence that chemotherapy will improve the survival rate. If chemotherapy is recommended, it is administered every three weeks via intravenous injection by our oncologist for a total of four to five treatments. The treatments are typically done on an outpatient basis and may take a total of 90 minutes to complete each visit. Unlike humans, most dogs do not lose their hair and usually have only mild side effects from the medication such as transient loss of appetite and vomiting.

The grade of the tumor, based on the biopsy report, will have a dramatic impact on the long-term survival times. Grade I and II synovial cell sarcomas are commonly cured with survival times exceeding three years. Grade III synovial cell sarcomas generally have a high rate of tumor metastasis and reported median survival times of seven months. Special stains of the biopsies can also be done to help differentiate the specific types of joint tumors and predict potential patient survival.

Short-term complications following surgery are uncommon and may include temporary dehiscence (opening) of the incision, bleeding and infection. Local recurrence is uncommon with amputation of the limb, unless the tumor involves a joint that cannot be removed with large margins. Metastatic disease is always a potential complication, therefore chest X-rays are recommended every three months for the first year, then once every six months thereafter.

For more information on this subject, speak to the veterinarian who is treating your pet.