Most of the targeted therapies for both canine and human osteosarcoma to date have focused on signalling pathways that appear to be overactive in OSA tumours, such as human epidermal growth factor receptor 2 (HER2), insulin-like growth factor 1 (IGF1) and mammalian target of rapamycin (mTOR) signalling [66]. This evidence concerns the gene ERBB2 and osteosarcoma.