In canines, IHC has been used to identify HER2 protein overexpression (i.e., being classified as HER2 positive) in several tumour types, including mammary carcinomas (28–40%), intestinal carcinomas (80%), rectal carcinomas (42%), and anal sac gland carcinomas (80%) [195,196,197,198]. The gene discussed is ERBB2; the disease is rectal carcinoma.