Proliferative activity of myoepithelial cells in normal salivary glands and adenoid cystic carcinomas based on double immunohistochemical labeling

Objective: To investigate the proliferative activity of myoepithelial cells (MEC) in normal salivary glands (NSG) and adenoid cystic carcinomas (ACC)) Study design. Twenty -three salivary gland specimens (13 ACC, 10 NSG) were studied using double immunohistochemical labeling for a smooth muscle actin (a-SMA) and proliferative cell nuclear antigen (PCNA)). Results: There was a significant difference in PCNA reactivity in normal samples between myoepithelial cells of the parotid glands and of the submandibular glands, rates being higher in the latter. Neoplastic myoepithelial cells exhibited higher expression than neoplastic epithelial cells. In addition, myoepithelial cells of the cribriform type of ACC showed PCNA reactivity lower than those of the tubular type, whereas there was no statistically significant difference in epithelial cell rates. We could not identify myoepithelial cells in solid pattern due to α-SMA negativity; although high PCNA reactivity was evident. Conclusion: These data suggest that the myoepithelial cell has a key role in ACC oncogenesis, more so than its epithelial cell counterparts. Moreover, the data provide a histopathological interpretation for aggressive clinical features of submandibular ACC, as the myoepithelial cells were less differentiated as compared to those of parotid glands.