Fig 1: Inhibition of both PLK1 and EGFR is more effective than inhibition of either target alone in ER NSCLC xenograft models. Mice bearing PC9-ER9 xenograft tumors with volumes of 150 mm3 were treated with volasertib and/or erlotinib or with vehicle controls(A) Tumor volume was measured twice weekly and significantly decreased after combination treatment. After 3 weeks of treatment, the mice were humanely killed. Resected tumors were subjected to immunohistochemical analysis for Ki67 (C) and caspase 3 (B) protein expression, which was scored and quantitated.