Cytokeratin expression by sarcomas does not indicate synovial origin in dogs

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 (<i>P</i> = .64) and neither sarcoma location (<i>P</i> = .76) nor cytokeratin expression (<i>P =</i> .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.