Expression and prognostic significance of CK19 in canine malignant mammary tumours Adelina Gama a , Anabela Alves a , Fernando Schmitt b,c, * a Department of Veterinary Sciences, CECAV, University of Trás-os-Montes and Alto Douro (UTAD), 5001-811 Vila Real, Portugal b Institute of Molecular Pathology and Immunology of the University of Porto (IPATIMUP), 4200-465 Porto, Portugal c Department of Pathology, Medical Faculty, University of Porto, Porto, Portugal article info Article history: Accepted 1 February 2009 Keywords: Canine Malignant mammary tumours Cytokeratin 19 Prognosis abstract Expression of the luminal cytokeratin CK19 was examined in 102 canine mammary carcinomas by immu- nohistochemical analysis and associated with known expression of oestrogen receptor (ER), basal/myo- epithelial cell markers, proliferation and survival. Negative staining for CK19 was present in 23.5% of tumours and was associated with histological type, grade, invasiveness, Ki67 index and expression of basal/myoepithelial cell markers. Positive staining for CK19 was associated with ER expression. Reduced expression of CK19 was associated with both shorter overall and disease-free survival rates; however, CK19 was not an independent prognostic factor in multivariate analysis. Reduced expression of CK19 in canine mammary carcinomas is related to an aggressive phenotype and may play a role in tumour progression. Ó 2009 Elsevier Ltd. All rights reserved. Introduction Mammary gland tumours are one of the most common neo- plasms in the female dog and are known for their biological and histomorphological heterogeneity (Ferguson, 1985; Nerurkar et al., 1989; Moulton, 1990). Several immunohistochemical studies have demonstrated the diagnostic value of specific luminal and ba- sal/myoepithelial cell markers in canine mammary tumours (Hell- mén and Lindgren, 1989; Griffey et al., 1993; Vos et al., 1993a,b; Espinosa de Los Monteros et al., 2002; Gama et al., 2003, 2004). The incidence of canine neoplasia appears to be increasing and the veterinary pathologist is required to determine a precise diag- nosis, as well as to assess prognosis (Zaidan Dagli, 2008). Cytokeratin (CK) is one of the three types of intermediate fila- ments that constitute the cytoskeleton of mammalian epithelial cells (Moll et al., 1982; Chu and Weiss, 2002). CKs are expressed in epithelial cells in a developmentally regulated and differentia- tion dependent manner (Romano et al., 1988; Bocker et al., 2002; Chu and Weiss, 2002). Simple epithelia express CKs of low molec- ular weight, whereas stratified epithelia contain high molecular weight CKs. In the normal human breast, the majority of luminal cells ex- press CK7, CK8, CK18 and CK19, whilst basal/myoepithelial cells express CK5, CK14, CK15 and CK17 (Bocker et al., 2002). Consider- ing that all of these cells can undergo malignant change, breast car- cinomas can be classified as expressing a luminal or a basal phenotype (Sorlie et al., 2001; Abd El-Rehim et al., 2004), with sev- eral studies describing a significant association between basal phe- notype and poor prognosis (van de Rijn et al., 2002; Abd El-Rehim et al., 2004). In canine mammary tissues, we and others have described the expression of a number of cell differentiation markers, such as CKs (Hellmén and Lindgren, 1989; Destexhe et al., 1993; Griffey et al., 1993; Vos et al., 1993a,b,c; Rabanal and Else, 1994), p63 (Gama et al., 2003; Ramalho et al., 2006), P-cadherin (Gama et al., 2004, 2008), a-smooth muscle actin (SMA) (Destexhe et al., 1993; Vos et al., 1993a,b,c) and calponin (Espinosa de los Monteros et al., 2002). CK8, CK18 and CK19 are considered to be luminal cell markers (Griffey et al., 1993; Vos et al., 1993a,b,c; Rabanal and Else, 1994), whereas CK5, CK14 and CK17 (Griffey et al., 1993; Vos et al., 1993a,b,c), p63 and P-cadherin (Gama et al., 2003, 2004, 2008) are expressed by basal/myoepithelial cells. SMA and calponin are exclusively expressed by myoepithelial cells (Destexhe et al., 1993; Vos et al., 1993a,b,c; Espinosa de los Monteros et al., 2002). On the basis of immunohistochemical expression of CK14, Grif- fey et al. (1993) has applied the term ‘basal carcinoma’ to canine mammary carcinomas. As with human breast cancer, these carci- nomas exhibit aggressive clinical behaviour (Griffey et al., 1993). However, to the best of our knowledge, no studies have associated CK expression in canine mammary tumours with prognosis. Re- cently, down-regulation of luminal cytokeratins CK18 and CK19 has been identified as a significant predictor of aggressive disease in human breast cancer patients (Woelfle et al., 2004; Parikh et al., 1090-0233/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.tvjl.2009.02.001 * Corresponding author. Address: Institute of Molecular Pathology and Immu- nology of the University of Porto (IPATIMUP), 4200-465 Porto, Portugal. Tel.: +351 22 5570700; fax: +351 22 5570799. E-mail address: fernando.schmitt@ipatimup.pt (F. Schmitt). The Veterinary Journal 184 (2010) 45–51 Contents lists available at ScienceDirect The Veterinary Journal journal homepage: www.elsevier.com/locate/tvjl