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Resource Library: Synovial Cell Sarcoma

VariableMedian disease-free
interval (months)
Histologic grade:
Cytokeratin staining:
Synovial cell sarcoma is a malignancy of mesenchymal tissue lining the joint. This is a rare tumor in animals, but occurs most commonly in large, but not giant, breed dogs. Presumably, this cancer can occur in any joint of the body, but is most commonly located at or near one of the major weight-bearing joints. The most commonly involved joint is the stifle, followed in decreasing order by the elbow, shoulder, tarsus, carpus and hip.

This tumor is most commonly diagnosed after the animal is presented because of lameness. There is frequently a nonpainful palpable mass located near one of the major weight-bearing joints. The mass is usually firm, but may have soft, fluctuant areas. The degree of lameness is correlated with the degree of bony involvement seen radiographically.

In one study, 22% of dogs had metastatic disease present at the time of diagnosis. However, metastasis is known to occur even after treatment has begun resulting in an overall metastasis rate between 20% and 50%. When metastasis occurs it is most commonly to the lungs and lymph nodes. However, metastasis has been reported to occur in the kidneys, spleen, thoracic pleura, liver and heart. Local recurrence (following surgery) and metastatic disease are common developments. Some dogs, however, will remain tumor free after amputation. Most treatment modalities involve amputation of the affected limb alone or in combination with some adjuvant therapy. Local resection without amputation fails to cure.

The two most important prognostic indicators for dogs with synovial cell carcinoma are the histologic grade and whether the specimen stains positive for cytokeratin or not. By looking at the prepared slides, a pathologist is able to give a tumor a histologic grade: 1, 2 or 3. The grade of the tumor can be useful in predicting the survival time for a dog diagnosed with synovial cell carcinoma. Dogs with grade 1 tumors had median survival times greater than 48 months. Those with grade 2 had median survival times of 36 months. Dogs with grade 3 tumors had a median survival time of 7 months.

Cytokeratin is a protein that is associated with epithelial tissue. When epithelial tissue is present in this particular tumor, this is correlated with an increase in aggressive behavior by the tumor. Dogs with tumors that stained positively for cytokeratin had a median survival time of 4 months while those who did not stain positively had a median survival time of greater than 48 months.

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