Expression of Ki-67, P63, P40, and alpha-smooth muscle actin in salivary gland carcinomas with or without myoepithelial differentiation

Abstract

Background: Myoepithelial cells are involved in the development of salivary glands. Many studies propose that these cells can prevent cell proliferation. Aim: This study aimed to investigate the expression of Ki-67, P63, P40, and alpha-smooth muscle actin (α-SMA) in salivary gland carcinomas with or without myoepithelial differentiation. Methods: A panel of myoepithelial markers including P63, P40, α-SMA, and Ki-67 were used for immunohistochemical study in 67 salivary gland carcinomas (33 with and 34 without myoepithelial differentiation). The percentage of positive cells was calculated (in high-power field) from a minimum of 1000 neoplastic cells. SPSS software (version 21) was used. Results: There was no statistically significant difference between Ki-67 expression and the presence or absence of myoepithelial cells (P = 0.6), but Ki-67 expression was related to the age (P = 0.032) and location of carcinomas (P = 0.001). All carcinomas with myoepithelial differentiation exhibited consistent P63+/P40+ staining, whereas polymorphous adenocarcinomas showed P63+/P40− immunophenotype. The expression of Ki-67 in adenoid cystic carcinomas was higher than mucoepidermoid carcinomas (P = 0.020) and polymorphous adenocarcinomas (P = 0.002). Conclusion: In the present study, although the decrease in the number of myoepithelial cells was associated with increased proliferation in adenoid cystic carcinomas, no such relationship was found in the overall assessment between the two groups. This can be justified by the fact that the clinical behavior of salivary carcinomas and their cell proliferation may be affected by factors other than the presence of myoepithelial cells or lack thereof. Ki-67 and P63/P40 expressions may be useful to differentiate adenoid cystic carcinomas from polymorphous adenocarcinomas in small biopsies.