ERBB2 and osteosarcoma: When described, it relied mainly on the general mechanism of drugs/combination activity in cancers rather than on specific osteosarcoma targets (for example, mammalian target of rapamycin [mTOR] inhibitors) or on the relative expression level of osteosarcoma cell surface protein with little knowledge about its mechanistic role (for example, anti-GD2, anti-HER2).