Myoepithelial cells in canine mammary tumours

•Review of methods of identification of myoepithelial cells in the canine mammary gland.•Role of myoepithelial cells in the genesis of mixed mammary tumours of dogs.•Myoepithelial cells and prognosis of canine mammary carcinoma: tumour-suppressor or progressor.•Role of myoepithelial cells in in situ growths of the canine mammary gland. Mammary tumours are the most common neoplasms of female dogs. Compared to mammary tumours of humans and cats, myoepithelial (ME) cell involvement is common in canine mammary tumours (CMT) of any subtype. Since ME cell involvement in CMT influences both histogenetic tumour classification and prognosis, correct identification of ME cells is important. This review describes immunohistochemical methods for identification of canine mammary ME cells used in vivo. In addition, phenotypic and genotypic methods to isolate ME cells for in vitro studies to analyse tumour-suppressor protein production and gene expression are discussed. The contribution of ME cells to both histogenetic classifications and the prognosis of CMT is compared with other species and the potential use of ME cells as a method to identify carcinoma in situ is discussed.