Finally, we demonstrate that the combination of VSVΔ51 and T-DM1 significantly improves survival in a human xenograft model of trastuzumab-resistant breast cancer (Fig. 3a) and increases VSVΔ51 growth specifically in HER2-overexpressing ovarian cancer cells derived from ascites obtained from patients (Fig. 3b–e, Supplementary Fig. 9). Here, ERBB2 is linked to breast carcinoma.