CURRENTTOPICSINBREASTPATHOLOGY The morphological spectrum of salivary gland type tumours of the breast MARIA P. FOSCHINI,LUCA MORANDI,SOFIA ASIOLI,GIANLUCA GIOVE, ANGELO G. CORRADINI AND VINCENZO EUSEBI Unit of Anatomic Pathology at Bellaria Hospital, Department of Biomedical and Neuromotor Sciences, University of Bologna, Bologna, Italy Summary Salivary gland like tumours of the breast constitute a wide spectrum of entities each one showing peculiar features and clinical behaviour. They can be subdivided as follows: (1) tumours showing pure myoepithelial cell differentiation, such as pure benign and malignant myoepitheliomas; (2) tumours with mixed epithelial and myoepithelial cell dif- ferentiation, such as pleomorphic adenoma, adenomyoe- pithelioma and adenoid cystic carcinoma; and (3) tumours with pure epithelial cell differentiation, such as acinic cell carcinoma, oncocytic carcinoma, mucoepidermoid carci- noma and polymorphous adenocarcinoma. These tumours share similar features with the salivary gland counterparts, but different clinical behaviour. Most salivary gland type tumours of the breast are negative for oestrogen and progesterone receptor and lack HER2 gene amplification, therefore they are classified as ‘triple nega- tive’ tumours. Nevertheless, some of the malignant entities (such as classical adenoid cystic carcinoma) exhibit good behaviour and do not need any treatment in addition to local control. The aim of the present paper is to review the morpholog- ical and prognostic features of salivary gland like tumours of the breast, in order to highlight the correct clinical management. Key words: Myoepithelium; myoepithelioma; adenomyoepithelioma; pleomorphic adenoma; adenoid cystic carcinoma; acinic cell carcinoma; oncocytic carcinoma; mucoepidermoid carcinoma; polymorphous adenocarcinoma. Received 29 July, revised 23 October, accepted 30 October 2016 Available online: xxx INTRODUCTION Breast and salivary glands structurally are both tubulo-acinar glands and, as expected, share some tumours due to their similar morphology. The first author who underlined the similarities between tumours of the breast and salivary glands was Azzopardi, who devoted to this subject an entire chapter of the book ‘Problems in Breast Pathology’. 1 Thereafter a great amount of work was done, leading to the concept that a wide spectrum of salivary glands tumours, both benign and malignant, show the same morphological features in the breast, but different clinical behaviour. These differences, if not well known in clinical practice, can lead to incorrect treatment. The aim of the present paper is to review most of the recently published papers that focus on similarities and dif- ferences between tumours of the salivary glands also shared by the breast. The main purpose is to highlight the correct clinical management. Tumours of the salivary glands can affect the breast and can be classified in three main groups: 2 (1) tumours showing pure myoepithelial cell differentiation; (2) tumours with mixed epithelial and myoepithelial cell differentiation; and (3) tumours with pure epithelial cell differentiation. TUMOURS WITH PURE MYOEPITHELIAL CELL DIFFERENTIATION Benign myoepithelioma (BME) BME is a tumour entirely composed of myoepithelial cells, resembling a benign smooth muscle tumour. 3 BME is a very rare lesion; it was originally described by Toth 4 and subse- quently by Enghardt and Hale. 5 Since then additional single cases have been reported. 4 – 9 BME usually affects female patients, forming small solid to cystic nodules. 5 Histology BME can show an intraductal growth pattern or present nodular architecture. It is composed of spindle to polygonal cells. Absence of cytological atypia, atypical mitoses and necrosis are useful to distinguish BME from a malignant lesion (Fig. 1A). Immunohistochemistry BME has to be differentiated from the several benign spindle cell lesions of the breast, among which myofibroblastoma 10 and leiomyomas are the most similar lesions. 11,12 Immuno- histochemistry demonstrating myoepithelial differentiation is important to drive the correct diagnosis. BMEs are typically positive for myoepithelial cell markers, such as high molec- ular weight keratins, p63, smooth muscle actin, calponin (Fig. 1B) and caldesmon. At a variance from leiomyoma that does not express keratins, BME is desmin negative. Prognosis The outlook of BME is generally favourable. Exceptions are the one case that recurred three times reported by Enghardt Print ISSN 0031-3025/Online ISSN 1465-3931 © 2016 Royal College of Pathologists of Australasia. Published by Elsevier B.V. All rights reserved. DOI: http://dx.doi.org/10.1016/j.pathol.2016.10.011 Pathology (- 2016) -(-), pp. 1 – 13 Please cite this article in press as: Foschini MP, et al., The morphological spectrum of salivary gland type tumours of the breast, Pathology (2016), http:// dx.doi.org/10.1016/j.pathol.2016.10.011