Epithelial-mesenchimal transition in canine mammary tumours: the role of myoepithelial cells

Introduction: In malignant epithelial tumours the epithelial-mesenchymal transition (EMT) phenomenon is reported. In the mammary gland, two cell types are present: luminal epithelial and basal myoepithelial cells, the latter hypothesized as being precursors of mesenchymal tissue. A panel of immunohistochemical markers of myoepithelial cells was applied to four different types of neoplasms with the aim of testing the role of myoepithelial cells in EMT in mammary tumours of the dog. Materials and Methods: Monoclonal and polyclonal antibodies specific for ER, p63, vimentin (VIM) and a-smooth muscle actin (a-SMA) were used on mammary gland neoplasms (five benign and three malignant myoepitheliomas, eight carcinomas in mixed tumours and nine complex carcinomas) and an algorithm was built to characterize the resting and the motile phenotype of myoepithelial cells. Results: ER labelled some basal (resting) and stellate (motile) myoepithelial cells. Myoepithelial markers, namely p63, VIM and a-SMA, labelled basal myoepithelial cells. Stellate myoepithelium lost the labeling with p63, but maintained positivity for VIM and a-SMA, which are also typical of EMT. Conclusions: This affinity, together with the increased transition of myoepithelium from resting basal to motile stellate cells, may be indicative of a transition from polarized immotile myoepithelial cells into highly migratory fibroblast-like cells.