Expression of alpha-smooth muscle actin in salivary mucoepidermoid and adenoid cystic carcinomas: A comparative immunohistochemical study.

BACKGROUND: Alpha-smooth muscle actin (α-SMA) is crucial in fibrogenesis. Salivary gland tumor types exhibit varying degrees of α-SMA expression because myoepithelial cells play diverse roles in their formation. The present study compared the immunohistochemical expression of α-SMA in mucoepidermoid and adenoid cystic carcinoma according to the grades and variants. METHODOLOGY: Sections of formalin-fixed, paraffin-embedded tissue blocks obtained from 50 cases of salivary gland carcinoma from 2011 to 2021 were stained using α-SMA monoclonal antibodies for immunohistochemical analysis. RESULTS: The mean α-SMA scores did not differ significantly among the three mucoepidermoid carcinoma histology levels. No notable variations in α-SMA expression were observed in the mucoepidermoid carcinoma cases analyzed. By contrast, high-grade adenoid cystic carcinoma cases had substantially higher α-SMA scores than cases with low or intermediate grades. The α-SMA scores did not differ significantly between the low and intermediate grades. Among the histological variants, more cases with highly significant α-SMA scores were found in solid types compared with tubular, cribriform, or combined types. Furthermore, patients with cribriform growth had significantly higher α-SMA scores than those with tubular tumor growth. Overall, the percentage of high reactivity (expression) (α-SMA score 4+) was significantly higher in adenoid cystic carcinoma cases than mucoepidermoid carcinoma cases. CONCLUSIONS: These findings highlight the importance of α-SMA as a tumor marker for differentiating between mucoepidermoid and adenoid cystic carcinoma in terms of the tumor grading, histological variant, and expression.