Plasmacytoid cells in salivary pleomorphic adenoma. An alternative interpretation of their immunohistochemical characteristics highlights function and capability for epithelial-mesenchymal transition

Publication date: Available online 7 February 2019

Source: Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology

Author(s): Ioannis G. Koutlas, Michelle Dolan, Mark W. Lingen, Prokopios P. Argyris

Abstract

Objectives

Plasmacytoid cells (PLCs) in salivary pleomorphic adenoma (SPA) are regarded as modified neoplastic myoepithelia and define plasmacytoid myoepithelioma (pMYO). However, histochemically, immunohistochemically and ultrastructurally, PLCs fail to demonstrate frank myogenous properties. Epithelial-mesenchymal transition (EMT) may explain the phenotypes in SPA. Our aim was to evaluate 1) PLCs with accepted or purported myoepithelial and EMT-related markers; and 2) pMYOs for PLAG1 aberrations by FISH.

Study Design

Eight SPAs with or without PLC-predominance and 3 pMYOs were immunohistochemically studied.

Results

PLCs in SPA and pMYO exhibited strong, scattered to diffuse positivity for K7, rare K14 positivity and were mostly negative for α-SMA, h-caldesmon, and p63/p40. S100 staining was strong and diffuse, while calponin was variable. DOG1 was negative. PLCs in pMYO and PLC-rich-SPA exhibited selective or diffuse, WT-1 and D2-40 immunoreactivity. EMT markers SNAIL/SLUG exhibited strong and variable immunoreactivity in PLCs, in contrast to weak or absent e-cadherin expression. SOX10 was diffusely and strongly positive. PLAG1 rearrangement was present in 1 pMYO.

Conclusions

1) PLCs mostly fail to express myoepithelial markers; 2) PLCs are neoplastic cells adapting to micro-environmental changes and capable of EMT; 3) Tumors composed solely of PLCs are apparently SPAs depleted of a ductal component.

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