Immunohistochemical assessment of HRAS Q61R mutations in breast adenomyoepitheliomas.

Fresia Pareja,Raluca Mihai,Mahsa Vahdatinia,Britta Weigelt,Pier Selenica,Sarat Chandarlapaty,Austin Szatrowski,Edi Brogi,Zsuzsanna Varga,Marcia Edelweiss,Felipe C Geyer ,Brian P Rubin ,Ian O Ellis ,Achim A Jungbluth ,Jorge S Reis‐Filho ,Maria Pia Foschini ,Ana Paula Martins Sebastião ,Michael S Toss ,Hannah Y Wen ,Edaise M Da Silva ,Emad A Rakha

doi:10.1111/his.14057

Abstract

Breast adenomyoepitheliomas (AMEs) are uncommon tumours. Most oestrogen receptor (ER)-positive AMEs have mutations in phosphoinositide 3-kinase (PI3K) pathway genes, whereas ER-negative AMEs usually harbour concurrent mutations affecting the HRAS Q61 hotspot and PI3K pathway genes. Here, we sought to determine the sensitivity and specificity of RAS Q61R immunohistochemical (IHC) analysis for detection of HRAS Q61R mutations in AMEs. Twenty-six AMEs (14 ER-positive; 12 ER-negative) previously subjected to massively parallel sequencing (n=21) or Sanger sequencing (n=5) of the HRAS Q61 hotspot locus were included in this study. All AMEs were subjected to IHC analysis with a monoclonal (SP174) RAS Q61R-specific antibody, in addition to detailed histopathological analysis. Nine ER-negative AMEs harboured HRAS mutations, including Q61R (n=7) and Q61K (n=2) mutations. Five of seven (71%) AMEs with HRAS Q61R mutations were immunohistochemically positive, whereas none of the AMEs lacking HRAS Q61R mutations (n=17) were immunoreactive. RAS Q61R immunoreactivity was restricted to the myoepithelium in 80% (4/5) of cases, whereas one case showed immunoreactivity in both the epithelial component and the myoepithelial component. RAS Q61R immunohistochemically positive AMEs were associated with infiltrative borders (P<0.001), necrosis (P<0.01) and mitotic index in the epithelial (P<0.05) and myoepithelial (P<0.01) components. RAS Q61R IHC assessment did not reveal Q61K mutations (0/2). IHC analysis of RAS Q61R shows high specificity (100%) and moderate sensitivity (71%) for detection of HRAS Q61R mutations in breast AMEs, and appears not to detect HRAS Q61K mutations. IHC analysis of RAS Q61R may constitute a useful technique in the diagnostic workup of ER-negative AMEs.

Highlights

Breast adenomyoepitheliomas (AMEs) are a heterogeneous group of lesions with dual epithelial and myoepithelial cell differentiation, classically composed of glandular epithelial structures surrounded by myoepithelial cell proliferation[1,2,3]
These findings show that the immunohistochemical detection of HRAS Q61R mutations in ERnegative breast AMEs is moderately sensitive (71%) and highly specific (100%), whereas in ERpositive AMEs, this antibody was of limited use as no cases were found to harbor HRAS Q61 hotspot mutations and/or RAS Q61R protein expression
Our findings show that IHC analysis has a high specificity and moderate sensitivity for identifying HRAS Q61R-mutated AMEs among estrogen receptor (ER)-negative cases

Summary

Introduction

Breast adenomyoepitheliomas (AMEs) are a heterogeneous group of lesions with dual epithelial and myoepithelial cell differentiation, classically composed of glandular epithelial structures surrounded by myoepithelial cell proliferation[1,2,3]. The World Health Organization (WHO) guidelines describe malignant forms of AME and some cases were reported in the literature[5, 8], but clear criteria to distinguish this entity from the spindle cell metaplastic carcinoma apart from identification of benign AME component in the tumor remain to be defined[1, 2]. It is our observation (EAR) that in a proportion of cases the concordance between morphology and immunoprofile of myoepithelial and epithelial cell components is low, making an accurate diagnosis and the distinction of each component a challenging task in such cases. Lack of definite diagnostic and molecular features of AME with their ambiguous nature and histogenesis leads to challenges in patients’ management and outcome prediction

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Conclusion