The distinction between sarcomatoid carcinoma (SC) and bona fide sarcoma can be difficult using conventional immunohistochemical markers. Epithelial-mesenchymal transition (EMT) has been proposed as a histogenetic mechanism for the development of SC. Expression of selected markers of EMT (Twist and Slug) was compared with other markers of epithelial differentiation in SC and spindle cell sarcoma to determine the utility of these antigens in this differential diagnosis. Twenty-seven cases of SC (excluding those of gynecologic origin) were stained by immunohistochemistry for cytokeratins (AE1/AE3, 5D3, CK5/6, and 34betaE12), p63, claudin-1, claudin-7, epithelial cadherin, placental cadherin, epithelial cell adhesion molecule/epithelial-specific antigen, 14-3-3sigma, Twist, and Slug. A comparison group of 21 spindle or pleomorphic spindle cell sarcomas was also studied. Immunohistochemical stains were scored in a semiquantitative manner and subsequent exploratory analyses were performed using logistic regression and chi2 tests. Only cytokeratin AE1/AE3 specifically labeled SC in a statistically significant manner. Other epithelial-specific markers tested did not distinguish SC from sarcoma primarily owing to low sensitivity. However, when positive, immunostains such as CK5/6, membranous epithelial cadherin, and nuclear p63 may aid in the distinction of SC from sarcoma. EMT markers were expressed in most cases of both SC and sarcoma, and were not useful in making a differential diagnosis between these neoplasms.