ERBB2 and neoplasm: Two representative KRAS wt, HER2 amplified, cetuximab resistant PDX tumors were treated with pertuzumab, an anti-HER2 monoclonal antibody preventing dimerization with HER partners including EGFR, in combination with either lapatinib, a dual EGFR/HER2 tyrosine kinase inhibitor, or cetuximab, and resulted in substantial and prolonged tumor regression, whereas pertuzumab alone had no effect.