ERBB2 and breast cancer: We first confirmed that the expression of full length HER2 in 4T1.2 cells (4T1.2-HER2 (20)) enabled increased VSVΔ51 spread following 4 hr pretreatment with T-DM1 to a similar extent as in JIMT1 human HER2+ breast cancer cells (Figures 1A–C).