Relative HER2 protein expression in normal canine tissue and canine osteosarcoma

Abstract

Development of HER2-targeted immunotherapy in canine osteosarcoma (OSA) is underway, yet HER2 expression in normal and neoplastic canine tissue has not yet been defined. This study's objective was to evaluate the relative HER2 protein expression in canine osteosarcoma tissue, normal canine tissue, and a HER2-overexpressing human cancer cell line. Flash frozen tumor tissue donated from 24 dogs with spontaneouslyoccurring OSA tumors, 2 normal colon samples, cell pellets from 2 OSA cell lines (Abrams, HMPOS) and a HER2-overexpressing human cell line were available for protein extraction and HER2 immunoblotting. Formalin-fixed tissue suitable for H and E staining and HER2 immunostaining was available for 6 normal colon and 18 OSA (13 primary tumors, 5 metastases) canine samples. None of the 26 OSA tumors showed relative HER2 blot band intensity equal to or greater than those of controls. Four of 5 OSA metastases and all 13 OSA primary tumors showed some degree of HER2 immunostaining, predominantly weak and cytoplasmic. Only a subset of spontaneously occurring canine osteosarcoma tumors express HER2 in a relevant manner for treatment with anti-HER2 immunotherapy, and not in a membranous pattern to justify surface-targeted therapies.