p63 as an Ideal Diagnostic Marker for Pleomorphic Adenoma: An Immunohistochemical Study

Abstract

Introduction: Pleomorphic Adenoma (PA) histopathologically represents a heterogeneous lesion with a varying proportion of epithelial and mesenchymal components. Due to its morphological diversity, a diagnostic dilemma often arises when identifying its various patterns. This diverse morphology is considered to be a function of the neoplastic myoepithelium. Tumor protein 63 (p63) is expressed in stratified epithelia and in the basal cells of salivary glands. Aim: To investigate the immunoreactivity of p63 as a reliable myoepithelial marker in PA. Materials and Methods: A cross-sectional study was performed in the Department of Oral and Maxillofacial Pathology at PGIDS, Rohtak, Haryana, India. The duration of the study was 14 months, from March 2015 to April 2016. A total of 15 tissue blocks of histopathologically diagnosed cases of PA were included from departmental archives and subjected to Immunohistochemistry (IHC) using a monoclonal p63 antibody. The myoepithelium was classified as myoepithelial-like (abluminal and spindled), modified myoepithelium (myxoid and chondroid), and transformed myoepithelium (solid epithelioid, squamous, and basaloid cribriform). IHC for p63 was assessed in each myoepithelial component, as well as in non neoplastic Myoepithelial Cells (MEC) and inner tubular epithelial cells. Only nuclear staining for p63 was considered positive. The obtained data were subjected to statistical analysis, and the Chi-square test was applied. Results: The PA samples subjected to IHC showed 100% p63 reactivity. Transformed MEC, abluminal, and modified MEC revealed variable immunostaining with a significant difference (p=0.049). There was no immunostaining in luminal/inner layer cells in all cases of PA. p63 was also expressed in the nuclei of MEC of acini and intercalated ducts of normal salivary gland tissue. Conclusion: p63 is a sensitive and specific myoepithelial marker to identify MEC in PA. Additionally, the expression of MECassociated markers in acini and intercalated ducts of normal salivary glands has confirmed their role in the histogenesis of this tumour.