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Sarcoma samples from 33 dogs, 25 subcutaneous and 8 articular, were submitted for cytokeratin immunohistochemistry. Eight of the 25 subcutaneous sarcomas (32%) expressed cytokeratin in 1% to 50% of the neoplastic cells. Of the 7 articular sarcomas evaluated, 1 (14%) expressed cytokeratin in 10% of neoplastic cells. The Kaplan-Meier survival analysis showed that the mean overall survival of dogs with subcutaneous sarcomas (28.1 months [confidence interval [CI]:17.8, 38.4]) did not significantly differ from those with articular sarcomas (24.8 months [CI = 0.5, 29.0]). Overall survival of dogs with sarcomas (both locations combined) immunoreactive for cytokeratin (31.2 months [CI = 17.8, 44.6]) did not differ from those not immunoreactive for cytokeratin (22.0 months [CI = 8.4, 35.6]). Therefore, cytokeratin expression does not indicate synovial origin (P =.64) and neither sarcoma location (P =.76) nor cytokeratin expression (P =.53) affects patient overall survival in this small study. The use of cytokeratin immunohistochemistry is not helpful to determine synovial origin of sarcomas in dogs. [ABSTRACT FROM AUTHOR]

The purpose of this review is to clarify the terminology, possible cells of origin, and expected behavior of the most common synovial tumors in dogs. The synovial lining consists of 2 cell types, type A and type B. Type A synoviocytes are histiocytes of bone marrow origin that are immunoreactive with antibodies against typical markers of histiocyte origin, such as CD18, Iba-1, and CD204. Certain breeds and dogs with previous injury to a joint, especially cranial cruciate ligament rupture, are predisposed to synovial histiocytic sarcoma. Type B synoviocytes are mesenchymal cells that produce synovial fluid. There are no specific markers of type B synoviocytes, but based on their gross and microscopic appearance, synovial myxosarcomas (previously considered synovial myxomas) are presumed to be of type B synoviocyte origin. These can infiltrate into surrounding tissues, but are slow-growing and rarely metastasize, and then only to regional lymph nodes. Synovial histiocytic sarcomas and myxosarcomas can cause lysis in multiple bones surrounding the joint, but they have different prognoses and require histopathology and sometimes immunohistochemistry to diagnose them. Synovial sarcoma and synovial cell sarcoma are terms used in the human medical literature for a tumor that is not of synovial origin; these terms should not be used in veterinary medicine. [ABSTRACT FROM AUTHOR]