Myoepithelial differentiation in cribriform, tubular and solid pattern of adenoid cystic carcinoma: A potential involvement in histological grading and prognosis.

Adenoid cystic carcinoma (AdCC) is known as a biphasic tumor composed of ductal and myoepithelial cells. The present study aimed to evaluate the amount and distribution of the myoepithelial cells in cribriform, tubular and solid subtypes of AdCC and analyze their relationship with histological grading and prognosis. A panel of myoepithelial markers including CK5/6, p63, p40, D2-40, calponin, α-SMA, S-100, and vimentin, together with a luminal cell marker CK7, and Ki-67 were used for immunohistochemical study in 109 AdCCs that included 38 cribriform, 36 tubular and 35 solid subtypes. The myoepithelial cells were labeled and found lined cystic-like paces, located at the periphery of the cribriform arrangements, and presented at the nonluminal cells of the two-layered tubular structures, while absent or dispersed in the solid pattern. Meantime, the solid subtype presented a higher proliferation rate assessed by mitotic count and Ki-67 labeling index, followed by poorer overall survival and recurrent-free survival. Furthermore, CK7 expression was found higher in solid pattern than in cribriform-tubular subtype, which showed negative correlation with the myoepithelial markers including D2-40, Calponin, α-SMA, p63, p40 and vimentin. The solid pattern of AdCC showed gland differentiation but loss of myoepithelial differentiation with a higher proliferation and more aggressiveness as well as poorer prognosis compared with the cribriform-tubular subtypes, which implies that loss of MEC differentiation might contribute to the poor prognosis of the solid subtype of AdCC. However, further studies are required to clarify its exact role in AdCC progression.