Human Epidermal Growth Factor Receptor 2 is Overexpressed in Canine Prostate Carcinoma

Human epidermal growth factor receptor 2 (HER2) is a cell surface receptor tyrosine kinase that belongs to the HER family. HER2 overexpression in human prostate cancer has been frequently observed; however, there are no reports on HER2 expression in canine prostate carcinoma (PC). The purpose of this study was to investigate HER2 expression and the underlying molecular mechanisms in canine PC. Twenty-one formalin-fixed paraffin-embedded canine prostate gland tissues (13 carcinomas and 8 normal controls) were analyzed for HER2 expression using immunohistochemistry. Using a digital polymerase chain reaction assay, the HER2 copy number in 8 PC and 6 normal prostate gland tissues was determined. HER2 overexpression occurred in 8/13 (61.5%) PC cases, but not in the normal controls. There were no significant associations between HER2 overexpression and clinical characteristics of the PC cases, such as age, neuter status, lymph node involvement, distant metastasis, and overall survival. HER2 copy number gain (CNG) was detected in 3/8 (37.5%) PC cases, but not in the normal controls. All PC cases with HER2 CNG exhibited HER2 overexpression, suggesting that HER2 CNG may lead to HER2 overexpression. These findings provide new insights into the molecular pathogenesis of canine PC; these may be therapeutically relevant. Dogs with PC would be useful as a preclinical large animal model for the development of new therapy for HER2-overexpressing prostate cancer in humans.