Expression and prognostic significance of CK19 in canine malignant mammary tumours

Abstract

Expression of the luminal cytokeratin CK19 was examined in 102 canine mammary carcinomas by immunohistochemical analysis and associated with known expression of oestrogen receptor (ER), basal/myoepithelial 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.

Introduction

Mammary gland tumours are one of the most common neoplasms 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 basal/myoepithelial cell markers in canine mammary tumours (Hellmén and Lindgren, 1989, Griffey et al., 1993, Vos et al., 1993a, Vos et al., 1993b, Espinosa de Los Monteros et al., 2002, Gama et al., 2003, Gama et al., 2004). The incidence of canine neoplasia appears to be increasing and the veterinary pathologist is required to determine a precise diagnosis, as well as to assess prognosis (Zaidan Dagli, 2008).

Cytokeratin (CK) is one of the three types of intermediate filaments 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 differentiation dependent manner (Romano et al., 1988, Bocker et al., 2002, Chu and Weiss, 2002). Simple epithelia express CKs of low molecular weight, whereas stratified epithelia contain high molecular weight CKs.

In the normal human breast, the majority of luminal cells express CK7, CK8, CK18 and CK19, whilst basal/myoepithelial cells express CK5, CK14, CK15 and CK17 (Bocker et al., 2002). Considering that all of these cells can undergo malignant change, breast carcinomas can be classified as expressing a luminal or a basal phenotype (Sorlie et al., 2001, Abd El-Rehim et al., 2004), with several studies describing a significant association between basal phenotype 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, Vos et al., 1993b, Vos et al., 1993c, Rabanal and Else, 1994), p63 (Gama et al., 2003, Ramalho et al., 2006), P-cadherin (Gama et al., 2004, Gama et al., 2008), α-smooth muscle actin (SMA) (Destexhe et al., 1993, Vos et al., 1993a, Vos et al., 1993b, Vos et al., 1993c) 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, Vos et al., 1993b, Vos et al., 1993c, Rabanal and Else, 1994), whereas CK5, CK14 and CK17 (Griffey et al., 1993, Vos et al., 1993a, Vos et al., 1993b, Vos et al., 1993c), p63 and P-cadherin (Gama et al., 2003, Gama et al., 2004, Gama et al., 2008) are expressed by basal/myoepithelial cells. SMA and calponin are exclusively expressed by myoepithelial cells (Destexhe et al., 1993, Vos et al., 1993a, Vos et al., 1993b, Vos et al., 1993c, Espinosa de Los Monteros et al., 2002).

On the basis of immunohistochemical expression of CK14, Griffey et al. (1993) has applied the term ‘basal carcinoma’ to canine mammary carcinomas. As with human breast cancer, these carcinomas 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. Recently, 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., 2008). We sought to evaluate the immunohistochemical expression of CK19 in malignant canine mammary tumours and its possible correlation with some relevant clinicopathological parameters, namely proliferation, oestrogen receptor (ER) status, basal/myoepithelial cell markers and survival, in order to investigate its possible value as a prognostic marker in canine mammary cancer.