Mesenchymal to Epithelial Transition in Canine Perivascular Wall Tumours (PWTS): Preliminary Assessment

Introduction: Mesenchymal to epithelial transition (MET) has been correlated to reduced invasiveness and improved prognosis in human sarcomas. MET is characterized by acquisition of an epithelial-like phenotype by expression of specific molecules such as cytokeratins, β-catenin and E-cadherin by neoplastic mesenchymal cells. Canine perivascular wall tumours (PWTs) display a more favourable prognosis compared with other soft tissue sarcomas. Our hypothesis is that MET development may partially explain PWTs distinctive behaviour. The aim of this work was to explore the occurrence of MET by the preliminary assessment of specific marker expression by immunohistochemistry (IHC) in canine PWTs. Materials and Methods: A series of 53 canine spontaneous PWTs were routinely processed, graded histologically and stained with anti-pan-cytokeratin (AE1/AE3), anti-β-catenin and anti-E-cadherin. Immunolabelling was reported as membranous, cytoplasmic or nuclear. For each subcellular localization, the percentage of positive neoplastic cells was recorded. IHC results were analysed against histological grade. Results: PWTs included were grade 1 (32/53), grade 2 (17/53) and grade 3 (4/53). Variable nuclear and cytoplasmic expression of E-cadherin (51/53) and β-catenin (52/53) was observed. All cases were AE1/AE3 negative. Expression did not correlate significantly with histological grade. Conclusions: The lack of membranous E-cadherin and of cytokeratins contrasted with our hypothesis and possibly excludes MET development in PWTs. E-cadherin expression in PWTs was considered aberrant as it is not constitutively expressed by normal vascular mural cells. The expression of β-catenin may reflect activation of the canonical Wnt/β-catenin pathway in PWTs.