Double-immunostaining of p63 protein and cytokeratin 8 in pleomorphic adenomas

Salivary gland pleomorphic adenoma (PA) has morphological diversity in tumor cell arrangements within its characteristic myxochondroid stroma, although it remains uncertain whether neoplastic myoepithelial or ductal cells are responsible for such diversity. To analyze the morphological and functional characteristics of the constituent cells of salivary gland PA, we investigated comparative expressions of p63 gene products (P63) as a myoepithelial/basal cell marker as well as those of cytokeratin 8 (CK8) as a duct epithelial cell marker through the use of double-immunohistochemical staining. Formalin-fixed, paraffin-embedded sections of 10 samples each of PA and normal salivary gland were examined. In normal salivary glands, P63-positive myoepithelial cells were distinguished from CK8-positive luminal cells of intercalated ducts. In PA, P63-positivity was observed in both luminal and basal cells of ductal structures, in spindle-shaped cells scattered in the myxoid stroma, and in peripheral cells of squamous-metaplastic foci, while CK8 was only positive in luminal cells of the ductal structures. Based on the simultaneous labeling of the two markers on same sections through double immunostaining, the ductal structures in PA were shown to be not functionally the same as normal ducts, and hence it is possible to consider that most of the PA cells shared myoepithelial phenotypes.