Increased Survival in Dogs with Malignant Mammary Tumours Overexpressing HER-2 Protein and Detection of a Silent Single Nucleotide Polymorphism in the Canine HER-2 Gene

The aims of this study were to explore the relationship between clinical outcome and HER-2 protein expression in dogs with malignant mammary tumours after surgery and to determine the sequence of the HER-2 gene. Tissues from 91 dogs diagnosed with malignant mammary tumours, six with benign lesions and two normal mammary glands were analysed for the expression of HER-2 by immunohistochemistry (IHC). Exons 14-18 of the HER-2 gene were amplified by reverse transcriptase polymerase chain reaction and sequenced in 19 tumours with IHC scores >2+; larger coding regions of HER-2 were analysed in five tumours. HER-2 protein overexpression was found in 27/91 (29.7%) of canine malignant mammary tumours. Dogs with HER-2-overexpressing malignant mammary tumours tended to have a higher survival rate than those that expressed a normal level of HER-2 within 2 years of surgery. In 3/19 cases, HER-2 sequences had a single nucleotide polymorphism, T(1725)C, with no change in the amino acid identity (Cys). No other sequence aberration of HER-2 was found.