Immunohistochemical Screening of HER2 in Canine Carcinomas: A Preliminary Study

SIMPLE SUMMARY: The human epidermal growth factor receptor-2 (HER2) has been studied in many human carcinomas. This receptor can be amplified and overexpressed in tumoral cells and serve as a prognostic, therapeutic, and predictive biomarkers. In human medicine there are many target drugs direct against this receptor, and these drugs are able to improve the clinical outcome of the patients. The overexpression of this receptor is mainly evaluated by immunohistochemistry, a technique that allows to evaluate the expression of the receptor on the cell surface. Recently, HER2 expression has been investigated in several canine tumors, but its role in the development of canine carcinoma is an object of debate. In this study we wanted to investigate the expression of HER2 protein in different histotypes of canine carcinomas in order to identify potential tumors that could benefit from the HER2-targeted therapy. We confirmed the hypothesis that HER2 is involved in tumor development of several canine carcinomas, amongst which carcinomas of the intestinal tract predominate. In dogs included in this study, 80% of intestinal carcinomas and a high proportion of rectal carcinomas (42%) were HER2 positive, suggesting that tumors of intestinal origin may potentially benefit from HER2-directed therapy. ABSTRACT: HER2 overexpression has been reported in various human and canine tumours. The aim of this study is to investigate the expression of HER2 protein in different histotypes of canine carcinomas in order to identify potential tumours that could benefit from the HER2-targeted therapy. Eighty-two (82) canine carcinomas (squamous cell, gastro-intestinal, rectal, pulmonary, prostatic, urothelial, and ovarian) from paraffin-embedded samp les were immunohistochemically evaluated. The degree of HER2 expression was scored based on the ASCO/CAP 2018 guidelines. Intestinal carcinomas were those with greater HER2 overexpression (3+) with 81% of positive cases, followed by 42% of rectal carcinomas and 28% of squamous cell carcinomas. These observations suggest that HER2 overexpression could be a driver in the oncogenesis of several types of canine carcinomas and lay the foundations for the identification of different types of canine carcinomas that could benefit from HER2-targeted therapy.