Protein Expression, Amplification, and Mutation of HER2 Gene in Canine Primary Pulmonary Adenocarcinomas: Preliminary Results

Simple Summary Canine lung adenocarcinomas are malignant tumors generally treated by surgical excision. When inoperable, chemotherapy can be performed with limited benefit. For this reason, the use of targeted drugs can be attempted, as has already happened in human medicine. In this retrospective study, 19 canine lung adenocarcinomas were investigated with three different methods to evaluate the expression of HER2. This transmembrane receptor for the human epidermal growth factor is often altered in human epithelial tumors, for which many targeted drugs have recently been produced. Using immunohistochemistry, fluorescence in situ hybridization, and next-generation sequencing, we found 3 cases out of 19 with protein overexpression, 2 cases with amplification, and only 1 case with a specific type of mutation (V659E), probably sensitive to tyrosine kinase inhibitory drugs. Due to the similar HER2 molecular changes in dogs and humans, this study provides preliminary information regarding the possible future use of targeted therapies in canine pulmonary adenocarcinomas. Recently, human epidermal growth factor receptor 2 (HER2) has emerged as a therapeutic target of interest for non-small-cell lung cancer in humans. The role of HER2 in canine pulmonary adenocarcinomas is poorly documented. To address this gap, this study employed three methodologies: immunohistochemistry (IHC), fluorescence in situ hybridization (FISH), and next-generation sequencing (NGS) to investigate the protein expression, gene amplification, and mutation of HER2 in 19 canine primary pulmonary adenocarcinomas. By IHC, 3 out of 19 cases were overexpressed 3+, 6 were 2+, and 10 were negative. With FISH, 2 cases were amplified (12.5%), 3 were inadequate for the analyses, and the others were non-amplified. With NGS, seven cases were inadequate. All other cases were wild-type, except for one IHC 3+ case, which was amplified with FISH and with a specific mutation already described in human pulmonary adenocarcinoma, V659E. This mutation is probably sensitive to tyrosine kinase inhibitory drugs. These results are similar to those in human medicine and to the few data in the literature on canine lung carcinomas; the presence of 12.5% of amplified cases in dogs lays the foundation for future targeted drugs against HER2 alterations.