Synovial sarcoma is a secondary bone tumor. It is considered secondary because it originates from metastatic bone dissemination (from neoplasms in other regions or from primary bone tumours) or from secondary bone invasion (due to the contiguity of the tumour to the bone).
| Secondary bone tumours |
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Metastatic
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Invasive, infiltrative
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Long considered the most frequent tumour localising to the synovium, synovial sarcoma originates from the synoviocytes of the joint capsule and tendon sheath.1 Recently, however, it has been shown that the incidences of histiocytic sarcoma and myxosarcoma are higher than that of synovial sarcoma.2 Synovial sarcoma must be differentiated from other tumours by immunohistochemical studies.
Synovial sarcoma affects middle aged (8.7 years) dogs of large breeds. No sex predilection has been reported and the most susceptible breeds include the Flat-Coated Retriever and Golden Retriever. Synovial sarcoma localises in the joints, especially in the knee and elbow (Fig. 1).
Clinically a swelling in the joints is noted and subjects show lameness. It is a locally invasive tumour and X-rays will reveal varying degrees of subchondral bone lysis, periosteal proliferation, and swelling of the peri-articular soft tissues. Changes are noticeable in the two articular heads, a feature that differentiates synovial sarcoma from primary bone tumours. Pathological fractures may also occur. This malignancy can metastasise to the lymph nodes and/or to the lungs: metastases have occurred in approximately 22-25% of the subjects at presentation.2,3
The diagnostic approach is similar to that described for appendicular osteosarcoma. It should be noted that synovial sampling is rarely diagnostic. Wide-margin surgery (amputation of the limb) is the treatment of choice. The mean survival of patients treated with amputation or resection with wide margins is 850 and 455 days, respectively.4 Chemotherapy (doxorubicin) and radiation therapy have been used as adjuvant treatment although their efficacy is unknown because of the insufficient number of cases studied.
The prognosis is influenced by clinical stage, histological grade, and extension of surgery. The median survival of dogs with lymph node or lung metastases at presentation is extremely short compared to that of dogs without metastasis (6 versus 36 months).3 Dogs with grade 3 synovial sarcoma have a shorter survival (7 months) than patients with grade 1 (48 months) or grade 2 (36 months) synovial sarcoma.3
Synovial sarcoma has also been reported in cats, with the characteristics of the tumour being similar to those reported in dogs except that secondary bone involvement is rare.5
References
- Craig, L.E., Julian, M.E., Ferracone, J.D., 2002. The diagnosis and prognosis of synovial tumors in dogs: 35 cases. Veterinary Pathology 39(1),66-73.
- Fairley, R., 2002. Synovial tumors in dogs. Veterinary Pathology 39(3),413-4.
- Fox, D.B,. Cook, J.L., Kreeger, J.M., Beissenherz, M., Henry, C.J., 2002. Canine synovial sarcoma: a retrospective assessment of described prognostic criteria in 16 cases (1994-1999). Journal of American Animal Hospital Association 38(4),347-55.
- Liptak, M.J., Forrest, L.J., 2007. Soft tissue sarcomas. In: Withrow, S.J., Vail, D.M. (Eds.),Withrow and MacEwen’s Small Animal Clinical Oncology. Saunders, Elsevier, St. Louis, MI, USA, pp. 425-454.
- Vail, D.M., Powers, B.E., Getzy, D.M., Morrison, W.B., McEntee, M.C., O'Keefe. D.A., Norris, A.M., Withrow, S.J., 1994. Evaluation of prognostic factors for dogs with synovial sarcoma: 36 cases (1986-1991). Journal of American Veterinary Medical Association205(9):1300-7.