ERBB2 and neoplasm: We carried out prospectively planned whole-exome sequencing of tumour biopsies at baseline and after progression on afatinib monotherapy to explore two questions: (1) what is the mutational landscape of HER2-positive IBC, and is it distinct from HER2-positive non-IBC; and (2) how does exposure to HER2 inhibition affect the evolution of IBC?