The role of Schwann cell differentiation in perineural invasion of adenoid cystic and mucoepidermoid carcinoma of the salivary glands.

Twenty cases of adenoid cystic carcinoma (ACC) and 18 cases of mucoepidermoid carcinoma (MEC), were examined for expression of the Schwann cell markers S100 protein and glial fibrillary acidic protein (GFAP) by immunohistochemical staining. The relationship between expression of S100 and GFAP and the occurrence of perineural invasion was assessed. Ultrastructural localization of S100 and GFAP was examined by immunoelectron microscopy, and the co-expression of S100 and muscle actin by double fluorescence immunostain. Perineural invasion was found in 11 ACCs (55%) and 0 MECs (0%). S100 and GFAP were expressed in most of the ACCs but none of the MECs; the difference in the rate of perineural invasion and expression of S100 and GFAP was significant between ACC and MEC (P<0.001). There was a correlation between the expression of S100 and GFAP and perineural invasion in salivary malignancy (P<0.001). The ultrastructures of S100- and GFAP-positive cells were consistent with the characteristics of myoepithelial cells. Double fluorescence immunostain also showed that S100 and muscle actin were expressed in the same type of ACC cells. These results indicate that Schwann cell differentiation correlates with perineural invasion in salivary malignancy, and occurs in modified myoepithelial cells of ACC.