p63 Expression of clear myoepithelial cells in epithelial-myoepithelial carcinoma of the salivary gland: a useful marker for naked myoepithelial cells in cytology

Abstract

Background: The typical form of epithelial-myoepithelial carcinoma (EMC) is a double-layered ductal structure, but occasionally EMC presents as a predominant solid growth of clear myoepithelial cells. In the current study, the authors analyzed the distribution and visual patterns of p63-positive clear myoepithelial cells in EMC.

Methods: Six cases of EMC were evaluated with Papanicolaou staining and with p63 and alpha-smooth muscle actin (SMA) immunostaining. Furthermore, the expressions of p63 and SMA were compared.

Results: The cytologic features of EMC were classified into two types-biphasic and clear cell-dominant type. The biphasic type showed myoepithelial cells with moderate or scant cytoplasm or naked nuclei, overlapping a cohesive cluster of ductal cells. This biphasic type was similar to that in fibroadenoma of the breast. The clear cell-dominant type consisted of myoepithelial cells with a large amount of fragile pale cytoplasm or naked nuclei. In this type, there were many clusters of myoepithelial cells without ductal cells. Nuclear immunoreactivity to p63 was expressed clearly in both biphasic and clear cell-dominant types. Cytoplasm immunoreactivity to SMA was expressed in many myoepithelial cells in the clear cell-dominant type, but only in myoepithelial cells with moderate cytoplasm in the biphasic type.

Conclusions: Clear myoepithelial cells in EMC were distributed in various patterns. The authors concluded that p63 is an especially useful marker of myoepithelial cells with naked nuclei in EMC.