Canine mammary mixed tumours: immunohistochemical expressions of EGFR and HER-2

BACKGROUND: Benign mixed tumours (BMTs) are frequently found in the mammary glands of female dogs, but the factors determining malignant transformation in these tumours are unknown. OBJECTIVE: To evaluate the expression of the oncoproteins, human epidermal growth factor receptor 2 (HER-2) and epidermal growth factor receptor (EGFR), in 46 carcinomas in BMTs (CBMTs) and to verify their possible association with the malignancy of the tumours. METHODS: Immunohistochemical expression was analysed in benign and malignant components separately, and then compared with 74 cases of BMTs. RESULTS: Among the CBMTs, positivity for HER-2 was found in the benign histological component of 4.3% (2/46), in the malignant epithelial non-invasive component of 14.8% (4/27) and in the malignant invasive epithelial component of 13.6% (6/44) of cases. Two of the 24 (8.3%) BMTs were positive for HER-2. There was no relationship between HER-2 and the tumour components. There was no significant difference between BMTs and CBMTs. Positivity for EGFR was found in the benign component of 17.4% (8/46) of the CBMTs, in the malignant epithelial non-invasive component of 40.7% (11/27%) and in the invasive epithelial malignant component of 45.4% (20/44). EGFR positivity was significantly associated with the invasive component of CBMTs. CONCLUSION: EGFR may contribute to malignant epithelial transformation of BMTs. In contrast, HER-2 overexpression may not be associated with the acquisition of a malignant epithelial phenotype.