ERBB2 and cancer: EGFR and ErbB2-targeting for molecularly defined cancers, such as EGFR-mutated lung adenocarcinomas and ErbB2-amplified breast and other cancers have demonstrated great promise but the emergence of acquired resistance limits long-term efficacy and better understanding of resistance mechanisms as well as identification of key downstream pathway activities and dependencies are pivotal for the design of novel strategies to prevent and combat resistance [13].