To assess the direct anti-cancer effects of trastuzumab and cetuximab on canine tumor cells expressing low levels of EGFR and/or HER-2, the cell viability of CMT-U334 and CF41.Mg cells was analyzed after treatment with trastuzumab (10 μg/ml) or cetuximab (10 μg/ml). The gene discussed is ERBB2; the disease is neoplasm.