Joint Cancer (Synovial Sarcoma) in Dogs

Synovial Sarcoma is a tumor of malignant nature originating from the synoviocytes (cells of the synovial memebrane) of the joint capsule (sac like fibrous tissue that envelops a synovial joint) and tendon sheath (sheet of membrane around a tendon). This is a soft-tissue tumor that arises from precursor cells outside the synovial membrane of the joint. Synovial cell sarcoma is a malignancy of mesenchymal tissue lining the joint. 

These locally invasive tumors have high metastasizing potential, spreading in more than 40% cases. 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 is a rare tumor in animals, but occurs most commonly in large, but not giant, breed dogs.

Swelling, pain and lameness in the affected joint are the common signs of synovial sarcoma. 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. Other common signs associated with synovial sarcoma include weight loss and no appetite (anorexia).

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